Who owns PRTA (PRTA)
Which tracked institutional funds hold PRTA, how they are positioned, and who is buying versus exiting — from SEC Form 13F-HR filings. See PRTA company fundamentals →
Ownership as of the 2026-Q1 13F filings. 13F is disclosed up to 45 days after quarter-end, so the most recent quarter fills in over the following weeks.
How the tape is positioned
30 tracked funds added or opened PRTA while 24 trimmed or exited it between 2025-Q4 and 2026-Q1 — the tape is split. When large holders disagree on a name, the funds moving first are sometimes ahead of the story.
A prompt to read the filings, not a verdict. 13F is a quarter-end snapshot disclosed up to 45 days late; a fund adds or exits for mandate, benchmark, and timing reasons that have nothing to do with a view on the stock. This is a starting question, not a signal to trade.
Conviction spread
PRTA’s largest tracked holder by dollar value, EcoR1 Capital, LLC, sizes it at 6.1% of its own reported 13F book, while the median holder sizes it at 0.0% of theirs — a 6.1pp conviction gap — its largest holder concentrates the name more heavily than the typical one.
Book-share is each fund’s reported value in PRTA divided by its whole reported 13F book, so it is comparable across funds of different sizes and is unaffected by stock splits. A higher share means a fund has committed more of its book to the name — a starting question about conviction, not a verdict or a signal to trade.
Institutional & insider positioning
Between 2025-Q4 and 2026-Q1, across 186 tracked filers holding PRTA, 99 increased or opened the position and 75 reduced or closed it; over the same quarter, there were no open-market insider Form 4s.
This fuses two public signals for the same quarter — how tracked institutions changed their positions and whether insiders bought or sold in the open market. It describes what was filed; it is a starting question, not a verdict or a signal to trade.
New buyers & exits
Funds opening or closing a position in PRTA between the 2025-Q4 and 2026-Q1 13F filings, and the largest changes among funds holding it in both. New buyers and exits are counted on fund presence (split-invariant); adds and trims are measured on reported value.
New buyers 6
- VANGUARD PORTFOLIO MANAGEMENT LLC$14M
- VANGUARD CAPITAL MANAGEMENT LLC$5M
- Penbrook Management LLC$3M
- VANGUARD FIDUCIARY TRUST CO$2M
- NORGES BANK$711K
- Jackson Creek Investment Advisors LLC$526K
Full exits 5
- VANGUARD GROUP INC$20M
- TWO SIGMA ADVISERS, LP$4M
- ARROWSTREET CAPITAL, LIMITED PARTNERSHIP$3M
- DIADEMA PARTNERS LP$1M
- Caption Management, LLC$583K
Largest adds
- Rubric Capital Management LP$13M
- BlackRock, Inc.$6M
- TWO SIGMA INVESTMENTS, LP$5M
- EverSource Wealth Advisors, LLC$3M
- MONIMUS CAPITAL MANAGEMENT, LP$2M
- Qube Research & Technologies Ltd$2M
Largest trims
- ARMISTICE CAPITAL, LLC$10M
- CITADEL ADVISORS LLC$4M
- Point72 Asset Management, L.P.$4M
- JANE STREET GROUP, LLC$3M
- STATE STREET CORP$3M
- JPMORGAN CHASE & CO$1M
Institutional holders
One row per tracked fund, largest reported value first. “% of value” is the fund’s share of this security’s tracked institutional value — not of shares outstanding. Rows marked stale are from an earlier filing than the security’s latest quarter — that fund is absent from the newest snapshot (position exited, or reported under a different name).
| Fund | Shares | Reported value | % of value | Quarter |
|---|---|---|---|---|
| FMR LLC | 7,551,218 | $73M | 10.9% | 2026-Q1 |
| Rubric Capital Management LP added | 5,000,000 | $49M | 7.2% | 2026-Q1 |
| BlackRock, Inc. added | 4,644,160 | $45M | 6.7% | 2026-Q1 |
| STATE STREET CORP trimmed | 1,938,498 | $19M | 2.8% | 2026-Q1 |
| D. E. Shaw & Co., Inc. added | 1,735,591 | $17M | 2.5% | 2026-Q1 |
| ADAR1 Capital Management, LLC added | 1,581,443 | $15M | 2.3% | 2026-Q1 |
| ACADIAN ASSET MANAGEMENT LLC added | 1,547,593 | $15M | 2.2% | 2026-Q1 |
| VANGUARD PORTFOLIO MANAGEMENT LLC new | 1,445,979 | $14M | 2.1% | 2026-Q1 |
| MORGAN STANLEY trimmed | 1,230,448 | $12M | 1.8% | 2026-Q1 |
| Palo Alto Investors LP trimmed | 1,208,568 | $12M | 1.7% | 2026-Q1 |
| TWO SIGMA INVESTMENTS, LP added | 1,205,978 | $12M | 1.7% | 2026-Q1 |
| GEODE CAPITAL MANAGEMENT, LLC added | 1,098,166 | $11M | 1.6% | 2026-Q1 |
| FEDERATED HERMES, INC. added | 1,059,849 | $10M | 1.5% | 2026-Q1 |
| JACOBS LEVY EQUITY MANAGEMENT, INC trimmed | 972,017 | $9M | 1.4% | 2026-Q1 |
| GOLDMAN SACHS GROUP INC trimmed | 818,885 | $8M | 1.2% | 2026-Q1 |
| DIMENSIONAL FUND ADVISORS LP added | 782,603 | $8M | 1.1% | 2026-Q1 |
| Nuveen, LLC added | 759,368 | $7M | 1.1% | 2026-Q1 |
| Qube Research & Technologies Ltd added | 614,603 | $6M | 0.9% | 2026-Q1 |
| RENAISSANCE TECHNOLOGIES LLC added | 607,515 | $6M | 0.9% | 2026-Q1 |
| Mariner, LLC trimmed | 563,082 | $5M | 0.8% | 2026-Q1 |
| MONIMUS CAPITAL MANAGEMENT, LP added | 485,617 | $5M | 0.7% | 2026-Q1 |
| VANGUARD CAPITAL MANAGEMENT LLC new | 484,126 | $5M | 0.7% | 2026-Q1 |
| Rangeley Capital, LLC trimmed | 449,460 | $4M | 0.6% | 2026-Q1 |
| Birchview Capital, LP added | 449,019 | $4M | 0.6% | 2026-Q1 |
| ARMISTICE CAPITAL, LLC trimmed | 439,411 | $4M | 0.6% | 2026-Q1 |
| CITADEL ADVISORS LLC trimmed | 435,574 | $4M | 0.6% | 2026-Q1 |
| BNP PARIBAS FINANCIAL MARKETS added | 424,596 | $4M | 0.6% | 2026-Q1 |
| Point72 Asset Management, L.P. trimmed | 399,830 | $4M | 0.6% | 2026-Q1 |
| BANK OF AMERICA CORP /DE/ trimmed | 393,632 | $4M | 0.6% | 2026-Q1 |
| Man Group plc added | 381,574 | $4M | 0.6% | 2026-Q1 |
| NORTHERN TRUST CORP added | 369,542 | $4M | 0.5% | 2026-Q1 |
| CHARLES SCHWAB INVESTMENT MANAGEMENT INC trimmed | 356,665 | $3M | 0.5% | 2026-Q1 |
| UBS Group AG trimmed | 328,491 | $3M | 0.5% | 2026-Q1 |
| EverSource Wealth Advisors, LLC added | 17,270 | $3M | 0.4% | 2026-Q1 |
| Walleye Capital LLC added | 277,168 | $3M | 0.4% | 2026-Q1 |
| Penbrook Management LLC new | 271,720 | $3M | 0.4% | 2026-Q1 |
| VANGUARD FIDUCIARY TRUST CO new | 254,573 | $2M | 0.4% | 2026-Q1 |
| Squarepoint Ops LLC added | 230,920 | $2M | 0.3% | 2026-Q1 |
| Focused Wealth Management, Inc added | 207,403 | $2M | 0.3% | 2026-Q1 |
| AQR CAPITAL MANAGEMENT LLC added | 196,700 | $2M | 0.3% | 2026-Q1 |
| Connor, Clark & Lunn Investment Management Ltd. added | 156,551 | $2M | 0.2% | 2026-Q1 |
| Quantinno Capital Management LP added | 144,299 | $1M | 0.2% | 2026-Q1 |
| Campbell & CO Investment Adviser LLC added | 142,587 | $1M | 0.2% | 2026-Q1 |
| Bank of New York Mellon Corp added | 136,322 | $1M | 0.2% | 2026-Q1 |
| MASSACHUSETTS FINANCIAL SERVICES CO /MA/ added | 132,051 | $1M | 0.2% | 2026-Q1 |
| Jump Financial, LLC trimmed | 118,936 | $1M | 0.2% | 2026-Q1 |
| JANE STREET GROUP, LLC trimmed | 107,926 | $1M | 0.2% | 2026-Q1 |
| Y-Intercept (Hong Kong) Ltd added | 100,805 | $980K | 0.1% | 2026-Q1 |
| Russell Investments Group, Ltd. added | 100,627 | $978K | 0.1% | 2026-Q1 |
| PRICE T ROWE ASSOCIATES INC /MD/ added | 95,649 | $930K | 0.1% | 2026-Q1 |
| XTX Topco Ltd added | 92,326 | $897K | 0.1% | 2026-Q1 |
| AMERIPRISE FINANCIAL INC trimmed | 89,212 | $867K | 0.1% | 2026-Q1 |
| Hennion & Walsh Asset Management, Inc. trimmed | 88,544 | $861K | 0.1% | 2026-Q1 |
| AMERICAN CENTURY COMPANIES INC added | 79,631 | $774K | 0.1% | 2026-Q1 |
| Assenagon Asset Management S.A. | 76,769 | $746K | 0.1% | 2026-Q1 |
| DCF Advisers, LLC trimmed | 73,247 | $712K | 0.1% | 2026-Q1 |
| NORGES BANK | 57,454 | $711K | 0.1% | 2026-Q1 |
| Creative Planning added | 72,986 | $709K | 0.1% | 2026-Q1 |
| Duncan Williams Asset Management, LLC | 70,281 | $683K | 0.1% | 2026-Q1 |
| MARTINGALE ASSET MANAGEMENT L P added | 69,101 | $672K | 0.1% | 2026-Q1 |
| ALLIANCEBERNSTEIN L.P. | 69,607 | $665K | 0.1% | 2026-Q1 |
| Susquehanna Portfolio Strategies, LLC added | 67,870 | $660K | 0.1% | 2026-Q1 |
| HSBC HOLDINGS PLC added | 65,070 | $632K | 0.1% | 2026-Q1 |
| PINNACLE ASSOCIATES LTD trimmed | 60,662 | $590K | 0.1% | 2026-Q1 |
| RHUMBLINE ADVISERS trimmed | 55,367 | $538K | 0.1% | 2026-Q1 |
| Jackson Creek Investment Advisors LLC new | 54,089 | $526K | 0.1% | 2026-Q1 |
| Rafferty Asset Management, LLC trimmed | 53,266 | $518K | 0.1% | 2026-Q1 |
| MILLENNIUM MANAGEMENT LLC added | 50,300 | $489K | 0.1% | 2026-Q1 |
| Quinn Opportunity Partners LLC | 50,000 | $486K | 0.1% | 2026-Q1 |
| EDGEWOOD MANAGEMENT LLC added | 50,000 | $486K | 0.1% | 2026-Q1 |
| Invesco Ltd. added | 49,808 | $484K | 0.1% | 2026-Q1 |
| Seven Fleet Capital Management LP | 43,300 | $421K | 0.1% | 2026-Q1 |
| PUBLIC EMPLOYEES RETIREMENT SYSTEM OF OHIO | 42,158 | $410K | 0.1% | 2026-Q1 |
| BARCLAYS PLC trimmed | 40,862 | $397K | 0.1% | 2026-Q1 |
| DEUTSCHE BANK AG\ added | 40,018 | $389K | 0.1% | 2026-Q1 |
| WINTON GROUP Ltd added | 34,700 | $337K | 0.1% | 2026-Q1 |
| FOX RUN MANAGEMENT, L.L.C. added | 35,052 | $324K | 0.0% | 2026-Q1 |
| EcoR1 Capital, LLC | 11,584,280 | $143M | 21.3% | 2025-Q1 stale |
| VANGUARD GROUP INC added | 2,140,909 | $20M | 3.0% | 2025-Q4 stale |
| Siren, L.L.C. added | 1,283,555 | $16M | 2.4% | 2025-Q1 stale |
| Boxer Capital Management, LLC | 690,000 | $9M | 1.3% | 2025-Q1 stale |
| Finepoint Capital LP trimmed | 640,071 | $8M | 1.2% | 2025-Q1 stale |
| ALGERT GLOBAL LLC added | 445,811 | $4M | 0.6% | 2025-Q3 stale |
| TWO SIGMA ADVISERS, LP added | 427,400 | $4M | 0.6% | 2025-Q4 stale |
| ARROWSTREET CAPITAL, LIMITED PARTNERSHIP trimmed | 298,101 | $3M | 0.4% | 2025-Q4 stale |
| Granahan Investment Management, LLC added | 461,082 | $3M | 0.4% | 2025-Q2 stale |
| NORDEA INVESTMENT MANAGEMENT AB added | 311,605 | $2M | 0.3% | 2025-Q2 stale |
| Cubist Systematic Strategies, LLC trimmed | 190,949 | $2M | 0.3% | 2025-Q3 stale |
| Janney Montgomery Scott LLC new | 106,898 | $1M | 0.2% | 2025-Q3 stale |
| DIADEMA PARTNERS LP new | 106,539 | $1M | 0.2% | 2025-Q4 stale |
| TD Asset Management Inc trimmed | 62,694 | $776K | 0.1% | 2025-Q1 stale |
| Monaco Asset Management SAM | 70,000 | $683K | 0.1% | 2025-Q3 stale |
| WELLINGTON MANAGEMENT GROUP LLP trimmed | 107,839 | $655K | 0.1% | 2025-Q2 stale |
| STATE OF WISCONSIN INVESTMENT BOARD added | 103,996 | $631K | 0.1% | 2025-Q2 stale |
| Caption Management, LLC | 61,009 | $583K | 0.1% | 2025-Q4 stale |
| Engineers Gate Manager LP added | 56,080 | $547K | 0.1% | 2025-Q3 stale |
| BALYASNY ASSET MANAGEMENT L.P. trimmed | 55,764 | $544K | 0.1% | 2025-Q3 stale |
| FRANKLIN RESOURCES INC trimmed | 47,251 | $451K | 0.1% | 2025-Q4 stale |
| DekaBank Deutsche Girozentrale | 14,000 | $383K | 0.1% | 2025-Q4 stale |
| Swiss National Bank trimmed | 56,500 | $343K | 0.1% | 2025-Q2 stale |
Ownership over time
Tracked institutional holder count and total shares held by filing quarter (independent scales). The curated-era tail and any mid-ingest latest quarter are handled honestly — a partial quarter is not drawn as a collapse.
Reading this table
Funds hold the same stock for different reasons — an index fund “holds” almost everything, an active manager sizes a name to a mandate and a benchmark, and each fund entered at its own price and time. Because 13F is filed up to 45 days after quarter-end, every row is a backward-looking snapshot; a manager may have traded since. Share-class siblings (a company’s A and C shares) are rolled up to one line so a dual-class name is never double-counted. Compare like-for-like. A large holder is not an endorsement, and a fund exiting is not a warning — this is a starting question, not a verdict.
About 13F filings
A Form 13F is a quarterly disclosure that institutional investment managers with over $100 million in US-listed equities must file with the SEC. In plain English: it is a snapshot of the long stock positions a fund held at the end of a quarter. It covers long US-listed equities only — not short positions, options, cash, or private holdings — and the funds shown are the large sample we track, not the complete 13F universe.