POSTER NO: 223

Brain-specific Sequence HMOB3 Is a Part of the 4,3KB 3'-Untranslated Region of the Human MAP1B Gene

Natalja M. Raevskaya, Lyudmila V. Dergunova, Irina P. Vladychenskaya, Svetlana A. Limborska
Institute of Molecular Genetics RAS, Kurchatov sq. 2, 123182 Moscow, Russia

Using in vitro and in silico approaches, we demonstrate that the Hmob3 brain-specific sequence is a part of the extended human MAP1B gene 3'UTR encoded by the yet unknown portion of the exon 7. Hmob3 clone was obtained previously by differential screening of the human medulla oblongata cDNA library and registered in EMBL-DataBank Database under the number Y09836. Our current data indicates that Hmob3 sequence is identical to a human chromosome 5 fragment (Acc. No AC012609), suggesting that the gene of interest (or its part corresponding to Hmob3) is localized within the named genomic clone. Search of the genomic sequence fragment upstream from the 5'-end of the region corresponding to Hmob3 against the EST GenBank database has revealed a large number of sequences similar to this fragment, whereas the 3'-end flanking genomic region has not shown any similarity to ESTs. Such a pattern of the transcription activity of this genomic fragment is consistent with the 3'-end of Hmob3 representing the 3'-end of the corresponding gene transcript. This idea is supported by the presence of the canonical polyadenylation signal AATAAA located 26 nucleotides upstream from Hmob3 poly(A) end. Further homology searches have positioned the genomic region corresponding to the 3'-end of the human MAP1B mRNA 1130 nucleotides upstream from 5'-end of the genomic region corresponding to Hmob3. Furthermore, the Hmob3 sequence is shown homologous to a mouse genomic clone (Acc. No AF115776) fragment which contains the 3'UTR of the MAP1B gene. Taken together, these data suggest Hmob3 to be a part of MAP1B mRNA 3'-untranslated region. To test this hypothesis, we carried out an expression analysis of the MAP1B human gene using the RT-PCR. Brain mRNA samples produced extended transcripts with their 5'-ends coinciding with MAP1B sequence and 3'-ends coinciding with Hmob3 (or with the genomic fragments flanking Hmob3 5'-region). Existence of such transcripts indicates that 3'-end MAP1B fragments and 5'-end Hmob3 fragments belong to the same gene. Based on the data obtained, we conclude that Hmob3 corresponds to a part of human MAP1B mRNA 3'untranslated region. Our results demonstrate that the 3'-untranslated region of MAP1B transcript has a length of 4330 nucleotides that significantly exceeds the length estimated previously. High similarity among the Hmob3 sequence contained within human MAP1B mRNA 3'UTR, the fragment of mouse MAP1B mRNA 3'UTR, as well as large number of anonymous ESTs coming from R. norvegicus, B. taurus and S. scrofa, confirms the existence of the longer transcripts of MAP1B and demonstrates the high phylogenetic conservatism of this gene.