Search for proteins interacting with Krr1p, a protein required for pre-ribosome assembly.

R. Gromadka and J. Rytka

Institute of Biochemistry and Biophysics, Polish Academy of Science, Pawiñskiego 5a, 02-106, Warsaw, Poland

The gene KRR1 (YCL059c) encodes a nucleolar protein essential for cell viability. The depletion of Krr1p leads to a drastic reduction of 40S ribosomal subunits due to defective 18S rRNA synthesis. The KRR1 gene was mutated in predicted nuclear localisation signal. The mutant did not grow at 18o C, which enabled a search for functional suppressors. The mutant strain was transformed with a S.cerevisiae genomic library on a multicopy vector and a cDNA library of S.pombe constructed in centromeric vector. Among the 10 genes isolated as multicopy suppressors of the mutation 4 are unknown ORFs, the function of the others is known although their role in ribosome biogenesis is obscure. The search for suppressors of the mutation with S.pombe cDNA library led mainly to the isolation of genes encoding ribosomal proteins.