New functions for Sub1 in RNAPII transcription regulation

COLLIN, ALEJANDRO; CALVO, OLGA

Salamanca

Congreso; III Meeting Red de Excelencia Temática: RNA Life; 2018

Red de Excelencia Temática:

Sub1 is an evolutionary conserved factor that was originally described as a transcriptional stimulatory protein based on its capacity to bind TFIIB, and due to conserved functional and structural features with human PC4. Recently, orthologues of PC4/Sub1 have been also identified in M. oryzae, and even in procaryotes. Sub1 has been implicated in many processes during mRNA biogenesis: (I) It is a functional component of the preinitiation complex. (II) ySub1/hPC4 links transcription initiation to termination and 3?-end processing, via the interaction with a polyadenilation factor. (III) Sub1 associates with Spt5 to influence transcription elongation rate. (IV) It globally modulates RNAP II-CTD phosphorylation, likely in in association with Rpb4/7 and the CTD phosphatase Fcp1. (V) Lately, it has been proposed a role for Sub1 during osmotic and oxidative stress. Apart from its multiple roles in mRNA transcription and processing, both Sub1 and PC4 are also involved in transcription by RNAPIII [4,5]. Moreover, PC4 and Sub1 have been implicated in other DNA-dependent processes beyond transcription, such as DNA repair and replication. Although many functions have been shown for Sub1, the exact molecular mechanisms through which it plays its different roles in mRNA biogenesis are mostly unknown. We have done novel discoveries about Sub1 that add new insight into its function during RNAPII transcription. Although Sub1 shows strong similarity to PC4, in particular at the level of their DNA binding domains, Sub1 is much larger. Specifically, it has an extra C-terminal domain with an unknown function, suggesting that Sub1 might have functional differences due to this additional domain. We have performed a detailed analysis of the ssDNA binding and C-terminal domains and identified the essential residues involved in Sub1 DNA binding capacity, which are not required during transcription elongation. Additionally, our data indicate that the C-terminus domain of Sub1, the function of which was previously unknown, might be important in promoting Sub1 release from the promoter to facilitate transcription elongation. In summary, Sub1 plays a dual function during transcription, being a pre-initiation factor via its DNA binding domain, and a transcription elongation factor through its C-terminus domain. Besides, we also have found that Sub1 levels are important for cell recovery from several stress conditions, and that they are regulated by the Srb10 kinase, a component of the Mediator CDK module.