PSL is a S-phase-related 55 kDa antigen which has been previously located inchromatin areas of the nucleus by electron microscopic studies. In the present report, weshow that it is released from purified HeLa cell nuclei by micrococcal nuclease treatment,which relieves chromatin under the form of nucleosome. However, the antigen is not associ-ated with nucleosomes but is part of a structure that sediments through 5-20% sucrosegradient. Moreover, PSL is completely retained on single-stranded DNA (ss-DNA) affini-ty columns and binds more efficiently HeLa cell ss-DNA than double stranded DNA.Although no direct evidence could be obtained, these data suggest that PSL might bea ss-DNA-binding or a RNA-binding protein.
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