Isolation and characterization of hrp1+, a new member of the SNF2/SWI2 gene family from the fission yeast Schizosaccharomyces pombe.

The SNF2/SWI2 ATPase/helicase family comprises proteins from a variety of species, which serve a number of functions, such as transcriptional regulation, maintenance of chromosome stability during mitosis, and various types of DNA repair. Several proteins with unknown functions are also included in this family. The number of genes that belong to this family is rapidly expanding, which makes it easier to analyze the common biological functions of the family members. This study was designed to clone the SNF2/SWI2 helicase-related genes from the fission yeast Schizosaccharomyces pombe in the hope that this would help to elucidate the common functions of the proteins in this family. The hrp1+ (helicase-related gene from S. pombe) gene was initially cloned by PCR amplification using degenerate primers based on conserved SNF2 motifs within the ERCC6 gene, which encodes a protein involved in DNA excision repair. The hrp1+ ORF codes for an 1373-amino acid polypeptide with a molecular mass of 159 kDa. Like other SNF2/SWI2 family proteins, the deduced amino acid sequence of Hrp1 contains DNA-dependent ATPase/7 helicase domains, as well as a chromodomain and a DNA-binding domain. This configuration is similar to that of mCHD1 (mouse chromo-ATPase/helicase-DNA-binding protein 1), suggesting that Hrp1 is a S. pombe homolog of mCHD1, which is thought to function in altering the chromatin structure to facilitate gene expression. Northern blot analysis showed that the hrp1+ gene produces a 4.6-kb transcript, which reaches its maximal level just before the cells enter the exponential growth phase, and then decreases gradually. DNA-damaging agents, such as MMS, MNNG and UV, decrease the rate of transcription of hrp1+. Deletion of the hrp1+ gene resulted in accelerated cell growth. On the other hand, overexpression of Hrp1 caused a reduction in growth rate. These results indicate that hrp1+ may act as a negative regulator of cellular growth.