Comparison of Chromatin Structure of Rat Mammary Glands between the Stages of Lactation and Regression after Weaning

Abstract

The chromatin structure of rat mammary glands was compared between two different developmental stages (5th day of lactation and 7th day of regression after weaning) when chromatin template activity for in vitro transcription declines more than twice. The DNA repeat length of the nucleosome was essentially unvariable between these stages (lactation, 195±7; regression, 198±10 nucleotide pairs). Gel electrophoresis of histones showed that histone H1 is more heterogeneous in regression than in lactation. The contents of the HMG proteins per DNA were much greater in the lactation than in the regression mammary gland.