INVOLVEMENT OF LYSINE-270 AND LYSINE-271 OF YEAST 5S RIBOSOMAL-RNA BINDING-PROTEIN IN RNA-BINDING AND RIBOSOME ASSEMBLY

Contributions of the highly conserved K270 and its neighboring K271 in the C-terminal region of the yeast ribosomal protein L1 to 5S rRNA bi nding and ribosome assembly were examined by in vivo and in vitro stud ies on the consequences of 14 substitution mutations. All mutant prote ins with a single amino-acid substitution at either position were able to bind 5S rRNA in vitro to an extent comparable to the wild-type. Ye ast cells expressing these mutant proteins, except the K270G mutant, g rew at nearly normal rates. Mutations of K270 appeared to produce more demonstrable effects than those of K271. The double mutant K270,271G bound RNA poorly and yeast cells expressing the mutant protein grew 30 % slower. Double mutants K270,271E and K270,271R were lethal, although the mutant protein was assembled into the 60S ribosomal subunits. The resultant subunits were not stable leading eventually to cell death T he in vitro RNA binding ability of the respective protein was reduced by 60% and 20%. Taken together, the present data identified K270 and K 271 as important amino-acid residues in the function of the yeast ribo somal protein L1.