Exchangeability of Qsr1p, a large ribosomal subunit protein required for subunit joining, suggests a novel translational regulatory mechanism.

Qsr1p is a 60S ribosomal subunit protein that is necessary for joining of large and small ribosomal subunits and is also one of the last proteins assembled onto the 60S ribosomal subunit in the cytoplasm. The finding that Qsr1p is identical to L7, a protein previously shown to cycle on and off large ribosomal subunits in the cytoplasm, suggests that the addition of Qsr1p onto the 60S ribosomal subunit could be utilized as a translational regulatory mechanism by limiting the supply of functional 60S subunits.