A HeLa-cell-encoded p21 is homologous to transcription elongation factor SII.

A 1.2-kb cDNA clone isolated from a HeLa cell library contains an open reading frame encoding a new protein (p21) of 21 kDa that is approx. 48% similar to members of the eukaryotic transcription elongation factor SII (TFIIS) family. The deduced amino-acid sequence of p21 indicates that it is hydrophilic, basic and contains nuclear localization signals, as well as multiple consensus phosphorylation sites.