Association of the 72/74-kDa proteins, members of the heterogeneous nuclear ribonucleoprotein M group, with the pre-mRNA at early stages of spliceosome assembly

Biochem J. 2002 May 1;363(Pt 3):793-9. doi: 10.1042/0264-6021:3630793.


We have investigated the role played in precursor mRNA (pre-mRNA) splicing by the protein pair of molecular size 72/74 kDa, which are integral components of a discrete subset of heterogeneous nuclear (hn) ribonucleoproteins (RNPs) named large heterogeneous nuclear RNP (LH-nRNP). This 72/74 kDa pair of proteins has been shown to belong to the hnRNP M group, and are referred to as 72/74(M). By applying specific immunoprecipitation assays in a consecutive series of splicing reactions in vitro, the antigenic 72/74(M) protein species were found to associate with the pre-mRNA and not the intermediate or final products of splicing. Kinetic studies, combined with isolation of pre-spliceosomal and spliceosomal complexes from the splicing reaction, indicated a loose association of 72/74(M) with both the initially formed H assembly and the first splicing-committed E complex. Stable binding was seen at a later stage of the reaction, well in advance of the appearance of the first intermediate products of RNA splicing. Evidence is provided that supports the almost exclusive association of 72/74(M) with pre-mRNA within the pre-spliceosomal A complex. This dynamic binding appeared to involve pre-mRNA sites similar to those of spliceosomal U1 and U2 small nuclear RNP complexes. Moreover, a preferential binding to a truncated RNA containing the 5' exon-intron part, rather than the intron-3' exon part, of pre-mRNA was observed.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Electrophoresis, Polyacrylamide Gel
  • HeLa Cells
  • Humans
  • Kinetics
  • Molecular Weight
  • Multigene Family
  • RNA Precursors / metabolism*
  • RNA Splicing
  • Ribonuclease T1 / metabolism
  • Ribonucleoproteins / metabolism*
  • Spliceosomes / metabolism*
  • Substrate Specificity


  • RNA Precursors
  • Ribonucleoproteins
  • Ribonuclease T1