Conserved and specific functions of mammalian ssu72

Abstract

We describe the cloning and characterization of a human homolog of the yeast transcription/RNA-processing factor Ssu72, following a yeast two-hybrid screen for pRb-binding factors in the prostate gland. Interaction between hSsu72 and pRb was observed in transfected mammalian cells and involved multiple domains in pRb; however, so far, mutual effects of these two factors could not be demonstrated. Like the yeast counterpart, mammalian Ssu72 associates with TFIIB and the yeast cleavage/polyadenylation factor Pta1, and exhibits intrinsic phosphatase activity. Mammals contain a single ssu72 gene and a few pseudogenes. During mouse embryogenesis, ssu72 was highly expressed in the nervous system and intestine; high expression in the nervous system persisted in adult mice and was also readily observed in multiple human tumor cell lines. Both endogenous and ectopically expressed mammalian Ssu72 proteins resided primarily in the cytoplasm and only partly in the nucleus. Interestingly, fusion to a strong nuclear localization signal conferred nuclear localization only in a fraction of transfected cells, suggesting active tethering in the cytoplasm. Suppression of ssu72 expression in mammalian cells by siRNA did not reduce proliferation/survival, and its over-expression did not affect transcription of candidate genes in transient reporter assays. Despite high conservation, hssu72 was unable to rescue an ssu72 lethal mutation in yeast. Together, our results highlight conserved and mammalian specific characteristics of mammalian ssu72.

Changes in Oxidative Stress Biomarker and Gene Expression Levels in Workers Exposed to Volatile Organic Compounds

“…Although biological functions of the 23 genes were largely unknown, many of the 23 genes have been reported to affect carcinogenesis and nervous system such as cognitive function and Parkinson's disease, areas that are known to be affected by chronic VOC exposure 2,3,9,11,25) .…”

Protein factors in pre-mRNA 3′-end processing

“…The human homolog of Ssu72p (hSsu72) has been identified as an interacting protein of the retinoblastoma tumor suppressor, Rb [225]. Similar to its yeast homolog, hSsu72 binds directly to TFIIB and Pta1p and exhibits phosphatase activity, but its role in 3′-end processing is still unknown.…”

“…Similar to its yeast homolog, hSsu72 binds directly to TFIIB and Pta1p and exhibits phosphatase activity, but its role in 3′-end processing is still unknown. hSsu72 cannot rescue a lethal mutation in Ssu72 in yeast [225]. A close homolog of hSsu72 is found in humans [222], sharing 72% sequence identity.…”

“…A close homolog of hSsu72 is found in humans [222], sharing 72% sequence identity. It has been suggested that this second isoform is encoded by a pseudogene [225].…”

RNA Polymerase II Phosphorylation and Gene Expression Regulation

“…In a screen looking for mammalian retinoblastoma tumor suppressors, a human homolog of yeast Ssu72 was identified. As in yeast, mammalian Ssu72 associates with TFIIB and the yeast cleavage/polyadenylation factor Pta1, and exhibits intrinsic phosphatase activity [176]. The crystal complex structure that is formed by human symplekin (Pta1 in yeast), hSsu72 and a CTD phosphopeptide has been elucidated, and hSsu72 was demonstrated to have a function in coupling transcription to pre-mRNA 3'-end processing [187].…”