Distribution studies on polytene chromosomes using antibodies directed against hnRNP.

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Abstract
The distribution of heterogeneous nuclear ribonucleoprotein (hnRNP) particles in Drosophila melanogaster polytene chromosomes was investigated using anti-B-36 serum. The use of polytene chromosomes allows resolution at the level of the chromomere and positive and negative correlations with transcriptional activity can be examined. The antiserum was obtained using the nuclear protein B-36 from Physarum polycephalum as the immunogen. It precipitated hnRNP particles from HeLa cells through a cross-reaction with the major 32,000 and 34,000 dalton hnRNP particle proteins. The antiserum cross-reacts with a Drosophila nuclear protein of .apprx. 34,000 daltons. By indirect immunofluorescence, the antiserum evidently reacts preferentially with transcriptionally active loci of the polytene chromosomes; loci previously or subsequently active do not show significant fluorescence. The overall pattern of fluorescence is very similar to that generated with anti-RNA polymerase B serum. The correlation of fluorescence and transcriptional activity observed suggests that the anti-B-36 serum is recognizing hnRNP proteins which have combined with nascent RNA molecules at the transcription sites.