A HYPERPHOSPHORYLATED FORM OF THE LARGE SUBUNIT OF RNA-POLYMERASE-II IS ASSOCIATED WITH SPLICING COMPLEXES AND THE NUCLEAR MATRIX

A hyperphosphorylated form of the largest subunit of RNA polymerase II (pol IIo) is associated with the pre-mRNA splicing process, Pol IIo w as detected in association with a subset of small nuclear ribonucleopr otein particle and Ser-Arg protein splicing factors and also with pre- mRNA splicing complexes assembled in vitro. A subpopulation of pol IIo was localized to nuclear ''speckle'' domains enriched in splicing fac tors, indicating that it may also be associated with RNA processing in vivo. Moreover, pol IIo was retained in a similar pattern following i n situ extraction of cells and was quantitatively recovered in the nuc lear matrix fraction. The results implicate nuclear matrix-associated hyperphosphorylated pol IIo as a possible link in the coordination of transcription and splicing processes.