KU-RELATED ANTIGENS ARE ASSOCIATED WITH TRANSCRIPTIONALLY ACTIVE LOCIIN CHIRONOMUS POLYTENE CHROMOSOMES

Antigens of Chironomus reactive with human sera containing anti-Ku ant ibodies and also with specific antibodies to each Ku subunit were char acterized by immunoblot analysis. Three main antigen species were iden tified in nuclear-enriched extracts from salivary gland cells of Chiro nomus thummi, ranging in M(r) from 55000 to 67000. The nuclear localiz ation of Ku-related antigens in the dipteran Chironomus was studied by immunofluorescent labeling in polytene chromosomes of the salivary gl ands. Balbiani rings, loci highly active in transcription, were found to be strongly labeled by anti-Ku antibodies. Sugar-induced changes in the activity of the Balbiani ring genes were accompanied by the redis tribution of Ku-related antigens as visualized by their absence in reg ressed Balbiani ring loci, and continued presence only in those that w ere transcriptionally active. A drastic change in the distribution of Ku-related antigens was also observed when C. thummi larvae underwent heat treatment as the immunofluorescent staining was restricted to pre viously described heat shock puffs. Anti-Ku sera reacted in addition w ith several chromosomal bands in which the presence of RNA polymerase IE was also immunologically detected. The results show that Chironomus antigens reactive with anti-Ku antibodies are related to transcriptio n in polytene chromosomes.