Unquestionably the most liquid point in interest rate markets is CME exchange-traded ten year note future. Because the basis between future and cheapest-to-deliver (CTD) bond cash price is relatively steady throughout the day, this provides a "knot" that determines the price of the belly of the curve.
Other "knots" may be from Fed Funds policy rate, and five/ten year benchmark cash bond prices. These bond prices are set according to supply and demand, for example, by E-Speed/BrokerTec digital exchanges. Market markers are given incentives to provide continuous liquidity on the exchange.
From these knots a cubic spline is used to generated a smooth Treasury yield curve - often new issue bonds or off-the-runs are priced as another basis to the splined curve rather than directly from current Treasuries.
As the market evolves, it may be that IRS provide more liquid knots than cash Treasury bonds due to the capital requirements of warehousing positions on balance sheet. In this case, we may in future see the 10y IRS become a driver of on-the run prices (e.g. 10y UST) as the swap-bond basis is similarly relatively steady.