MOLECULAR-CLONING OF CDNAS ENCODING VARIANTS OF MEIOTIN-1 - A MEIOTICPROTEIN ASSOCIATED WITH STRINGS OF NUCLEOSOMES

Meiotin-1 is a chromatin-associated protein, originally isolated from microsporocytes of Lilium longiflorum, which is found predominantly in cells undergoing meiotic prophase. Chromatin fractionation studies de monstrated that meiotin-1 has an unusual stoichiometry relative to tha t of histone H1 and the core histones in chromatin fibers. The protein is found less frequently than is histone H1, and appears to be distri buted once every 5 to 13 nucleosomes. This distribution may approximat e the number of nucleosomes per turn of the chromatin solenoid. A trun cated cDNA was identified by immunoscreening of an expression library, and the cDNA was used as a hybridization probe to select a full lengt h cDNA. Variations between the sequence of the predicted polypeptide a nd sequenced peptides, and variations between the amino acid compositi on of the protein and the deduced protein indicate that the cDNAs enco de minor variants of mature meiotin-1. RNA gel blot hybridization stud ies reveal that the meiotin-1 mRNA is restricted to anthers in which m eiosis is occurring. Computer analysis of the polypeptide deduced from the cDNA indicates that the protein begins with a region highly homol ogous to the conserved central globular domain of histone H1 molecules . DNA gel blotting experiments demonstrate that homologous sequences e xist in the genomes of a fern, a fungus, and both mono- and dicotyledo nous plants. Meiotin-1 has been evolutionarily conserved and I propose that it arose from histone H1 to fulfill a role in organizing meiotic chromatin.