A Protein Factor, ASF, Controls Cell-Specific Alternative Splicing of SV40 Early pre-mRNA in Vitro

Cell. 1990 Jul 13;62(1):25-34. doi: 10.1016/0092-8674(90)90236-8.


SV40 early pre-mRNA is alternatively spliced by utilization of two different 5' splice sites and a shared 3' splice site to produce large T and small t mRNAs. The ratio of small t to large T mRNAs produced in human embryonic kidney 293 cells is 10- to 20-fold greater than in other mammalian cells, suggesting the existence of a 293 cell-specific factor that modulates alternative splicing. Here we show that nuclear extracts from 293 cells give rise to significantly more small t splicing than do extracts from HeLa cells. Using an in vitro complementation assay, we have characterized and extensively purified a factor from 293 extracts that brings about striking increases in small t splicing with concomitant decreases in large T splicing. The factor is heat sensitive and micrococcal nuclease resistant, suggesting that it is a protein lacking an accessible RNA component. Purification of the alternative splicing factor indicates that the activity is contained in one of several possibly related polypeptides of 30-35 kd.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Biological Factors / isolation & purification
  • Biological Factors / metabolism*
  • Cell Line
  • Cell Nucleus / metabolism
  • Drug Stability
  • Genetic Complementation Test
  • HeLa Cells / metabolism
  • Humans
  • Introns
  • Molecular Weight
  • Plasmids
  • RNA Precursors / genetics*
  • RNA Splicing
  • RNA, Viral / genetics*
  • Simian virus 40 / genetics*


  • Biological Factors
  • RNA Precursors
  • RNA, Viral