ANALYSIS OF THE YEAST NSR1 GENE AND PROTEIN DOMAIN COMPARISON BETWEENNSR1 AND HUMAN HNRNP TYPE A1

The yeast nucleolar protein-encoding gene NSR1 was isolated by low-str ingency screening of a yeast genomic library with the human heterogene ous nuclear ribonucleoprotein type A1 (hnRNP A1) cDNA probe, and was m apped to chromosome VII. RNA abundance was determined and the transcri ption start point and polyadenylation site were mapped. A comparison b etween the Nsr1 and hnRNP A1 proteins, based on homopolymer RNA bindin g to their structural domains in vitro, revealed a striking biochemica l similarity. When the N-terminal, lysine- and arginine-rich domain of Nsr1 was removed, the truncated protein behaved similarly to hnRNP A1 ; furthermore, the two RRM (RNA recognition motif) domains of Nsr1 beh aved in the same manner as the two RRM domains of hnRNP A1. The bioche mical data, therefore, would support the hypothesis that the two RRM d omains in hnRNP A1 and Nsr1 interact with RNA in a similar manner in b oth mammalian and yeast cells, respectively.