A genome-wide survey of alternative translational initiation events in Homo sapiens

Alternative translational initiation is an important mechanism to increase the diversity of gene products. Although some of alternative translational initiation events have been reported, such information remains anecdotal and does not allow for any generalizations. The number of the known alternative translational initiation genes is so few that we know little about its mechanism. There is a great demand to discover more alternative translational initiation genes. However, it is arduously time-consuming to discover novel alternative translational initiation genes by the experimental method. Therefore we systematically analyzed protein sequences available in public database and predicted 1237 protein clusters as potential alternative translational initiation events. We concluded that about 8%—10% of human genes have alternative translational initiation sites. The results significantly increased the number of alternative translation initiation events and indicated that alternative translation initiation is an important and general regulation mechanism in the cellular process.

Novel Evidence Suggests Hepatitis B Virus Surface Proteins Participate in Regulation of HBV Genome Replication

Naturally occurring mutations in surface proteins of Hepatitis B virus(HBV) usually result in altered hepatitis B surface antigen(HBsAg) secretion efficiency.In the present study,we reported two conserved residues,M75 and M103 with respect to HBsAg,mutations of which not only attenuated HBsAg secretion(M75 only),but also suppressed HBV genome replication without compromising the overlapping p-gene product.We also found M75 and M103 can initiate truncated surface protein(TSPs) synthesis upon over-expression of full-length surface proteins,which may possibly contribute to HBV genome replication.However,attempts to rescue replicationdefective HBV mutant by co-expression of TSPs initiated from M75 or M103 were unsuccessful,which indicated surface proteins rather than the putative TSPs were involved in regulation of HBV genome replication.

The novel OCT4 spliced variant OCT4B1 can generate three protein isoforms by alternative splicing into OCT4B

OCT4 is one of the key transcription factors in maintaining the pluripotency and self-renewal of embryonic stem （ES） cells.Human OCT4 can generate two isoforms OCT4A and OCT4B by alternative splicing.OCT4B1 is a recently discovered novel OCT4 spliced variant,which has been considered as a putative marker of stemness.Compared with the OCT4B mRNA,OCT4B1 mRNA is generated by retaining intron 2 as a cryptic exon which contains a TGA stop codon in it.As a result,the protein product of OCT4B1 mRNA could be truncated.Interestingly,we present here that OCT4B1 can indirectly produce the same protein products as OCT4B.We have demonstrated that OCT4B1 mRNA can be spliced into OCT4B mRNA,and encode three protein isoforms.The splicing of OCT4B1 mRNA into OCT4B mRNA can be remarkably inhibited by the mutation of the classical splicing site.Our result suggests that OCT4B mRNA may originate from OCT4B1 mRNA by alternative splicing.