MEIOTIN-1, A MEIOSIS-ENRICHED PROTEIN PRESENT IN NORMAL LEPTOTENE CHROMOSOMES AND LACKING IN PRECOCIOUSLY CONDENSED LEPTOTENE CHROMOSOMES

During mitotic prophase, chromosomes progressively compact to their me taphase length. In contrast, meiotic chromosomes condense moderately u ntil late in prophase I, then they condense more dramatically (coil) t o their fully condensed state. Meiotin-1 is a meiosis-enriched, chromo somal protein. We propose that it delays coiling until after reciproca l genetic exchange. We have used immunoblotting and immunocytochemistr y with normal lily cells undergoing meiosis to demonstrate that meioti n-1 is present during the early portions of prophase I, but diminishes at the time when meiotic chromosomes begin to coil. Additionally, we have examined lily meiotic nuclei undergoing the reversible phenomenon of precocious leptotene chromosome condensation (precocious coiling). The leptotene chromosomes that are precociously condensed lack meioti n-1 immunostaining. Furthermore nuclei returning to the normal state o f moderate prophase I condensation acquire meiotin-1.