Sequence of cDNAs encoding components of vascular actin single-stranded DNA-binding factor 2 establish identity to Puralpha and Purbeta.

Transcriptional repression of the mouse vascular smooth muscle alpha-actin gene in fibroblasts and myoblasts is mediated, in part, by the interaction of two single-stranded DNA binding activities with opposite strands of an essential transcription enhancer factor-1 recognition element (Sun, S., Stoflet, E. S., Cogan, J. G., Strauch, A. R., and Getz, M. J. (1995) Mol. Cell. Biol. 15, 2429-2436). One of these activities, previously designated vascular actin single-stranded DNA-binding factor 2 includes two distinct polypeptides (p44 and p46) which specifically interact with the purine-rich strand of both the enhancer and a related element in a protein coding exon of the gene (Kelm, R. J., Jr., Sun, S., Strauch, A. R., and Getz, M. J. (1996) J. Biol. Chem. 271, 24278-24285). Expression screening of a mouse lung cDNA library with a vascular actin single-stranded DNA-binding factor 2 recognition element has now resulted in the isolation of two distinct cDNA clones that encode p46 and p44. One of these proteins is identical to Puralpha, a retinoblastoma-binding protein previously implicated in both transcriptional activation and DNA replication. The other is a related family member, presumably Purbeta. Comparative band shift and Southwestern blot analyses conducted with cellular p46, p44, and cloned Pur proteins synthesized in vitro and in vivo, establish identity of p46 with Puralpha and p44 with Purbeta. This study implicates Puralpha and/or Purbeta in the control of vascular smooth muscle alpha-actin gene transcription.