Yeast gene SRP1 (serine-rich protein): Intragenic repeat structure and identification of a family of SRP1-related DNA sequences☆

Abstract We have isolated and sequenced a yeast gene encoding a protein ( M r 24,875) very rich in serine (SRP) and alanine residues that accounted for 25% and 20% of the total amino acids, respectively. The SRP 1 gene is highly expressed in culture conditions leading to glucose repression (Marguet & Lauquin, 1986), the amount of SRP1 mRNA representing about 1 to 2% of total poly(A) + RNA. A repetitive structure of eight direct tandem repeats 36-base long, also reflected in the amino acid sequence, was found in the second half of the open reading frame. The consensus amino acid sequence of the repeat was Ser-Ser-Ser-Ala-Ala-Pro-Ser-Ser-Ser-Glu-Ala-Lys. Replacing the genomic copy of the cloned gene with a disrupted SRP 1 gene indicated that the SRP 1 gene was not essential for viability in yeast, but several SRP1 -homologous sequences were found within the yeast genome, raising the possibility that the disrupted SEP 1 gene is rescued by one of the other SRP-homologous sequences. Complete separation of yeast chromosomes by contour-clamped homogeneous field electrophoresis indicated that, apart from chromosome V, which carries the SRP 1 gene, 12 chromosomes have SRP-related sequences with various degrees of homology. These sequences were located on chromosomes XV, VII and XI under stringent conditions of hybridization ( t m −20 ° C ), and observed on chromosomes I, II, III, IV, VI, VIII, X, XI and XII, only under low-stringency conditions ( t m −40 ° C ). Northern blot analysis of both the wild type and SAP1 -disrupted strains indicated that along with SRP 1 at least one more member of the SRP family was transcribed to a 0.7 kb (1 kb = 10 3 bases) polyadenylated RNA species clearly distinct from the SRP 1-specific mRNA (1 kb long). Analyses of the SRP 1 repeat domain suggested a model for the divergent evolution of the repeats in the SRP1 sequence.