Short-term interest rates: PRSXX.US, being a money market fund, is heavily influenced by prevailing short-term interest rates. Increases in rates typically lead to higher yields and potentially price appreciation.

Federal Reserve policy: The Fed's monetary policy decisions, such as adjusting the federal funds rate, directly impact short-term interest rates and, consequently, PRSXX.US's performance.

Credit risk: While money market funds aim for safety, the creditworthiness of the securities they hold can affect returns. Downgrades in credit ratings may slightly depress prices.

Supply and demand: General supply and demand for money market funds can influence prices, although this impact is usually less significant than interest rate fluctuations.

Economic conditions: Overall economic health and inflation expectations can influence interest rate expectations and thus affect PRSXX.US.

Regulatory changes: Changes in regulations governing money market funds can influence the cost of managing the fund and potentially affect yields.