The amino acid sequence of neuropolypeptide h3 from Homo sapiens brain has been determined. It revealed that h3 is the exact counterpart of the 21-kDa protein from Bos taurus brain and the 23-kDa protein from Rattus norvegicus brain: The three proteins belong to the same 21-23-kDa protein family. Multiple tissue Northern blots showed that the mRNA encoding the 21-23-kDa protein is expressed in different amounts according to tissues and species; it is particularly abundant in Rattus norvegicus testis.

A 21 kDa protein purified from bovine brain cytosol was previously described as a hydrophobic ligand binding protein; however, its accurate biological function remained still uncertain. In order to get further information about its potential biological role, an extended prediction of its secondary and three dimensional structures was undertaken. We describe here a process which permitted us to discover a structural homology between the 21 kDa protein and the N-domain of yeast phosphoglycerate kinase (PGK). This process is based on comparing the 21 kDa protein with all the proteins presenting a slight homology, by using the Hydrophobic Cluster Analysis (HCA) method. According to the observed similarity between the N-domain of yeast PGK and the 21 kDa protein, we built a model which was shown to possess a potential binding site for nucleotides. Moreover, the model obtained presents three-dimensional (3D) structure similarity with adenylate kinase. These results suggest two main hypotheses: (i) the 21 kDa protein may belong to the kinase family; (ii) the binding of a nucleotide could imply a modification of the 3D structure of the 21 kDa protein that can promote the transfer of hydrophobic ligands to the plasma membrane. Meanwhile, verification of these hypotheses has been in part performed experimentally: the 21 kDa protein binds MgATP as well as, to a lesser extent, phosphoglycerate.

Myoneurin belongs to the BTB/POZ and zinc finger protein family whose members have been implicated in regulatory functions of gene expression. Myoneurin has been identified in various tissues, but muscle is a privileged site of myoneurin gene transcription. We examined the neuromuscular expression of myoneurin during development and after axotomy. Myoneurin expression is developmentally regulated in mouse muscle and appeared to be associated with neuromuscular junctions during the late embryonic period. Myoneurin is located in and around synaptic myonuclei in mouse and human adult muscle. The expression of myoneurin is dysregulated after nerve section. Thus, the restricted myoneurin expression in synaptic myonuclei appeared to be controlled by muscle electrical activity. Myoneurin is identified within the peripheral condensed chromatin and the euchromatin/heterochromatin regions, and thus fulfills structural and expression criteria to represent a synaptic gene regulator.

A cytosolic 23kDa protein was initially purified from bovine brain and shown to bind phosphatidylethanolamine. Later, it was also characterized in rat and human brain, and it is now known to be widespread, having been found in numerous tissues in several species. Here, we report the high level of mRNA and phosphatidyl ethanolamine binding protein expression in rat testis and to a lesser extent in mouse testis. In human testis, although it was not detectable by Northern blot analysis, the mRNA was shown to be present when PCR amplification was performed. Immunohistochemical experiments revealed that the testicular phosphatidylethanolamine binding protein (tPBP) is principally expressed in the elongated spermatids of both rat and mouse testis. This finding, and the association of tPBP with cellular membranes, suggest its possible implication in membrane remodelling during spermatid maturation.