Characterization of mouse reticulocyte free globin mRNP.

Globin messenger ribonucleoprotein particles (free and polysomal) from mouse reticulocyte lysates were characterized for their mRNA composition, translational activity as well as the proteins in direct contact with them. In contrast to the homogeneous single-peak distribution of rabbit and duck reticulocyte free mRNPs, mouse free mRNP particles were heterogeneously dispersed on the sucrose density gradient into two major domains called region I and region II. Region I appeared enriched with alpha-globin mRNP and region II with beta-globin mRNP. mRNP from both regions was translationally active. Examination of lysates prepared from beta-thalassemic mice revealed a reduction of translatable beta minor mRNP within region I, supporting the hypothesis of a compensatory recruitment of beta minor free mRNP into polysomes in beta-thalassemic mice.