PubMed · 2467411
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W J Lukiw, D R McLachlan. 1988. Silver stain image amplification.. https://doi.org/10.1016/0168-9525(88)90144-8
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The Structural Maintenance of Chromosome (SMC) protein family plays a central role in higher-order genome organization through ATP-dependent DNA loop extrusion by cohesin and condensin and other processes. Whether these activities fully account for the complexity of chromosome architecture remains unknown. Here, we uncover a conserved ATP-independent mechanism of chromatin condensation by SMC complexes, occurring via biomolecular condensation. Using single-molecule fluorescence imaging, we show that a variety of SMCs form dynamic DNA-bound condensates that exhibit key features of biomolecular condensates, including droplet coalescence, fluorescence recovery after photobleaching, and rapid exchange with free SMC complexes. Atomic force microscopy analysis of human cohesin-DNA assemblies reveals DNA-length-dependent clustering, providing evidence for bridging-driven condensation. Analyses of in vivo super-resolution imaging and high-throughput chromosome conformation capture (Hi-C) data indicate that these condensates form chromatin-associated clusters with multi-loop structures. Together, our results establish that SMC complexes employ ATP-independent phase condensation as well as ATP-dependent activities to shape genome architecture. This work reveals a broadly conserved principle of chromosomal organization across eukaryotes.
The SPT4, SPT5 and SPT6 genes of Saccharomyces cerevisiae were identified originally by mutations that suppress delta insertion mutations at HIS4 and LYS2. Subsequent analysis has demonstrated that spt4, spt5 and spt6 mutations confer similar pleiotropic phenotypes. They suppress delta insertion mutations by altering transcription and are believed to be required for normal transcription of several other loci. We have now analyzed interactions between SPT4, SPT5 and SPT6. First, the combination of mutations in any two of these three genes causes lethality in haploids. Second, some recessive mutations in different members of this set fail to complement each other. Third, mutations in all three genes alter transcription in similar ways. Finally, the results of coimmunoprecipitation experiments demonstrate that at least the SPT5 and SPT6 proteins interact physically. Taken together, these genetic and biochemical results indicate that SPT4, SPT5 and SPT6 function together in a transcriptional process that is essential for viability in yeast.
Proteins in the cytosol, postnuclear particulate, and nuclear fractions from seven specimens of normal prostate from bladder cancer patients, 14 specimens of benign hypertrophic prostate (BPH), and three specimens of cancerous prostate were analyzed and compared by SDS-polyacrylamide slab gel electrophoresis. Abundant protein species in the cytosol fractions were 60K (species having a molecular weight of about 60,000) and 42K; their relative contents were about 35% for 60K and about 12% for 42K. In the postnuclear particulate fraction, 42K was the most abundant (about 10% of the total). The contents of these major protein species were similar in specimens of normal and diseased prostates. In addition, there are marked similarities in the electrophoretic patterns for all the protein (24-29 species) in the cytosol and postnuclear particulate fractions of the human prostate, except for four minor species in the cytosol fraction. Of the nuclear proteins, the content of core histones (H2A, H2B, H3, and H4) was fundamentally similar among all the specimens, whereas the content of H1 histone was different from one specimen to another. The most remarkable and significant difference was that the 42K-NHP (nonhistone protein having a molecular weight of about 42,000), 55K-NHP, and 190K-NHP concentrations were significantly higher in BPH than in normal and cancerous prostates.