Abstract

Meiotin‐1 is a protein found in developing microsporocytes of Lilium longiflorum, and immunological assays indicate that cognates exist in both mono‐ and dicotyledonous plants. Its temporal and spatial expression pattern, coupled with its unusual distribution in chromatin and the properties it shares with histone H1, encourages speculation that it is involved in regulating meiotic chromatin structure. Molecular analyses provide support for the hypothesis that meiotin‐1 arose from histone H1 by an exon shuffling mechanism, as meiotin‐1 is an H1‐like protein that lacks the amino‐terminal domain shared by H1 molecules. We have proposed that meiotin‐1 serves to limit chromatin condensation in order to foster the unique cytological and molecular events which occur during meiotic prophase. As such, meiotin‐1 fits the role of a ‘meiosis readiness factor’, and its accumulation to a threshold level may commit mitotically dividing progenitor cells to differentiate into meiocytes.