Molecular characterization of a ribosome-associated Hsp70-homologous gene from Rhizopus nigricans

A ribosome-associated Hsp70-homologous gene (Rnssb-1) was isolated from the genomic library of the filamentous zygomycete fungus Rhizopus nigricans. The nucleotide sequence of a genomic clone encoded the N-terminal part of a protein with high similarity to the yeast SSB ribosome-associated chaperones. The missing 3' end of the gene was obtained by 3' RACE. The Northern blot analysis showed that the Rnssb-1 gene is constitutively expressed and is not induced upon heat shock at 37 degrees C. The primary structure analyses revealed that the coding region of the Rnssb-1 gene is interrupted by at least four introns. Their splicing was not inhibited by exposure of the organism to heat shock as proven by RT-PCR. A Southern blot analysis of R. nigricans genomic DNA confirmed the presence of two additional gene copies of ribosome-associated Hsp70 genes in the fungal genome.