Cytoplasmic protein binding to highly conserved sequences in the 3' untranslated region of mouse protamine 2 mRNA, a translationally regulated transcript of male germ cells.

Abstract

The expression of the protamines, the predominant nuclear proteins of mammalian spermatozoa, is regulated translationally during male germ-cell development. The 3' untranslated region (UTR) of protamine 1 mRNA has been reported to control its time of translation. To understand the mechanisms controlling translation of the protamine mRNAs, we have sought to identify cis elements of the 3' UTR of protamine 2 mRNA that are recognized by cytoplasmic factors. From gel retardation assays, two sequence elements are shown to form specific RNA-protein complexes. Protein binding sites of the two complexes were determined by RNase T1 mapping, by blocking the putative binding sites with antisense oligonucleotides, and by competition assays. The sequences of these elements, located between nucleotides +537 and +572 in protamine 2 mRNA, are highly conserved among postmeiotic translationally regulated nuclear proteins of the mammalian testis. Two closely linked protein binding sites were detected. UV-crosslinking studies revealed that a protein of about 18 kDa binds to one of the conserved sequences. These data demonstrate specific protein binding to a highly conserved 3' UTR of translationally regulated testicular mRNA.

Post–transcriptional control of gene expression during spermatogenesis

“…Synthesis of a translational activator, like a protein kinase or phosphatase that modifies the mRNP, is a possibility. The RNA-binding properties of TB-RBP appear to be coupled to its phosphorylation status 23,24 and are consistent with such a model. Of course, synthesis of a translational activator of the protamine mRNAs only tells us how activation of protamine translation is achieved.…”

“…To elucidate the mechanisms of translational regulation it is important to identify all of the factors involved. Despite significant progress in identifying protamine RNA-binding proteins, none of the proteins thus far described, PRBP, 41 TB-RBP, 23,24 or the 48r50 kDa Y box proteins, 39 have been shown to mediate the translational repression of the protamine mRNAs in vivo. Certain properties of these proteins, for example, the sequence-specific binding properties of the 48r50-kDa Y box proteins and TB-RBP, the ability of the binding site for the 48r50-kDa proteins to repress translation in vivo and the presence of the PRBP-binding site in a region of the Prm-1 3Ј UTR shown to be sufficient for translational repression in transgenic mice, are desirable for putative translational repressors.…”

Two salmon neuropeptides encoded by one brain cDNA are structurally related to members of the glucagon superfamily

“…Conservation between fish and mammals of 3' non-translated regions in other neuropeptide-gene families are usually restricted to only a few motifs [44]. Considering the evolutionary distance between fish and mammals, approximately 400 million years, the high conservation of the 3' non-translated sequence is probably related to the function of the 3' non-translated region in interactions of the mRNA with proteins that affect mRNP structure and translational control [45].…”

Expression of a gene duplication encoding conserved sperm tail proteins is translationally regulated in Drosophila melanogaster.

“…Several genes in the mouse and other mammalian species (including protamine 1 and 2 genes) are transcribed in round spermatids but are under translational control and will be translated only in elongated spermatids (17). For the protamine gene, the important region has been localized in the 3' UTR of the mRNA (4), and a protein specifically binding to this region has been identified (22). Whether this mammalian regulatory protein and the putative Drosophila counterpart are related remains to be determined.…”