IN POSTMEIOTIC MALE GERM-CELLS POLY(A) SHORTENING ACCOMPANIES TRANSLATION OF MESSENGER-RNA ENCODING GAMMA ENTERIC ACTIN BUT NOT CYTOPLASMICBETA-ACTIN AND GAMMA- ACTIN MESSENGER-RNAS

In the mammalian testis the cytoplasmic beta and gamma actins are expr essed in all stages of germ-cell differentiation, whereas gamma enteri c actin is expressed in germ cells solely in postmeiotic stages. North ern blot analysis of mouse testicular RNAs reveals actin mRNAs of abou t 2.1, 1.5, and 1.4 kB. The 2.1-kB mRNAs encode the cytoplasmic beta a nd gamma actins, whereas the two faster-migrating actin mRNAs encode g amma enteric actin. When postmitochondrial mouse testis extracts are f ractionated by sucrose gradient centrifugation, the 1.5-kB gamma enter ic actin mRNA is primarily found in the nonpolysomal fraction, whereas the 1.4-kB gamma enteric actin is polysomal. When the poly (A) tails are removed, the nonpolysomal and polysomal gamma enteric actin mRNAs both migrate at 1.3 kB, indicating that the difference in electrophore tic mobilities of the two gamma enteric actin mRNAs is caused by poly (A) length differences. The nonpolysomal and polysomal forms of the cy toplasmic beta and gamma actins show similar electrophoretic mobilitie s before and after deadenylation. Sequence comparison of the 3' untran slated region of the mouse gamma enteric actin to the 3' untranslated regions of other testicular mRNAs that undergo partial deadenylation r eveals three highly-conserved sequence elements. These data demonstrat e that the poly (A) shortening of polysomal mRNAs previously seen only with testis-specific mRNAs that are stored as mRNPs also occurs with mRNAs of widely-expressed genes that are expressed in postmeiotic male germ cells. The mRNAs all contain specific conserved sequence element s in their 3' untranslated regions. (C) 1996 Wiley-Liss, Inc.