Redistribution of U-snRNPs during mitosis.

In this study we examined the distribution of U-snRNPs during mitosis using a monoclonal antibody which recognizes the 28 kD protein associated with U-snRNP particles. During interphase U-snRNPs are concentrated within discrete intranuclear protein clusters. The onset of mitosis is accompanied by a breakdown of these nuclear protein clusters and U-snRNPs are redistributed between the condensing chromosomes. During metaphase and anaphase, two populations of U-snRNPs can be identified: those associated with the chromosome surface and a 'free' form distributed throughout the cytoplasm. During telophase, the reformation of nuclear protein clusters appears to be associated with the chromosome surface and coincides with chromatin decondensation. These studies suggest that the interphase assembly of nuclear domains containing U-snRNPs is sensitive to the transcriptionally active or decondensed state of chromatin.