The binding of the alpha subunit of protein kinase CK2 and RAP74 subunit of TFIIF to protein-coding genes in living cells is DRB sensitive

In a previous report, we documented that a major portion of the nuclear pro tein kinase CK2 alpha (CK2 alpha) subunit does not form heterooligomeric st ructures with the beta subunit, but it binds tightly to nuclear structures in an epithelial Chironomus cell line [1]. We report here that the CK2 alph a, but not beta, subunit is co-localized with productively transcribing RNA polymerase II (pol II) on polytene chromosomes of Chironomus salivary glan d cells. Likewise, the RAP74 subunit of TFIIF, a potential substrate for CK 2, is co-localized with pol II. The occupancies of chromosomes with the CK2 alpha and RAP74 subunits are sensitive to DRB, an inhibitor of pol II-base d transcription and the activity of CK2 and pol II carboxyl-terminal kinase s. DRB alters the chromosomal distribution of the CK2 alpha and RAP74 subun its: there is a time-dependent clearance from the chromosomes of CK2 alpha and RAP74 subunits, which coincides in time the completion and release of p reinitiated transcripts after addition of DRB. The results suggest that bot h the CK2 alpha and RAP74 subunits travel with the elongating pol II molecu les along the DNA template during the entire transcription cycle. No detect able re-association of CK2 alpha and RAP74 with the promoters takes, howeve r, place after the completion of the preinitiated transcripts in the presen ce of DRB. In contrast, the binding of hypophosporylated pol II and TFIIH t o the active gene loci is not abolished by the DRB regimen. Our data are co nsistent with the possibility that in living Chironomus salivary gland cell s, DRB interferes with the recruitment of TFIIF, but not of TFIIH, to the p romoter by interference with the activity of the CK2 alpha subunit enzyme a nd phosphorylation of RAP74 and thereby DRB blocks transcription initiation .