Localization of nuclear proteins related to high mobility group protein 14 (HMG 14) in polytene chromosomes

An antibody was raised against "high mobility group" nuclear protein 14 (HMG 14) from calf thymus, known to be associated with actively transcribed chromatin. By means of indirect immunofluorescence, it was shown to react with the nuclei of mouse fibroblasts and of brain cells from Xenopus and Drosophila, but not of Xenopus erythrocytes. The antibody was used to detect immunologically related proteins in giant chromosomes of the midge, Chironomus pallidivittatus. Indirect immunofluorescence with anti-HMG 14 antibody in polytene nuclei was restricted to the active puffs. Giant puffs (Balbiani rings) exhibited especially intense fluorescence in their peripheral regions. An inducible puff site, the Balbiani ring 6 locus, showed no reaction with the antibody prior to induction. When puff formation began, the chromosome site assumed a very intense fluorescence, which disappeared again when the Balbiani ring was recondensed. - Protein extracts of salivary gland nuclei were found on immunoblots to contain one major protein fraction that reacted with the anti-HMG 14 antibody. The electrophoretic mobility of this fraction was similar to that of calf thymus HMG 17. - It is concluded that actively transcribed puffs in polytene chromosomes contain HMG 14-related protein(s) that are not present in potentially active gene loci prior to induction.