Gene, 171(1996)307-308 8 1996 Elsevier Science B.V. All rights reserved. 0378-l 119/96/$15.00 GENE 09659 Isolation and sequencing of the 5’ end of the rat microtubule-associated protein (MAP 1B)-encoding cDNA * (Cytoskeleton; neuronal protein; axonal growth; gene expression) Dong Liu and Itzhak Fischer* Department of Neurobiology and Anatomy, Medical College of Pennsylvania and Hahnemann University, Philadelphia, PA 19129, USA Received by R.W. Davies: 7 July 1995: Accepted: 7 September 1995; Received at publishers: 29 January 1996 301 SUMMARY We have isolated and sequenced the 5’end of the cDNA encoding the rat microtubule-associated protein 1B (MAPlB). We found that this region is highly homologous to the corresponding regions of the human [Lien et al., 22 (1994) 273-2801 and mouse [Noble et al., J. Cell Biol. 109 (1989) 3367-33761 MAPlB genes. The combination of the sequence that we are presenting with the previously published sequence [Zauner et al., Eur. J. Cell Biol. 57 (1992) 66-741, represents the complete rat MAPlB cDNA coding sequence. Microtubule-associated protein 1B (MAPlB) is a developmentally regulated neuronal 340-kDa protein (Bloom et al., 1985). MAPlB is enriched in growing axons (Fischer and Romano-Clarke, 1991; Boyne et al., 1995) and is at low levels in adult brain except for regions that maintain synaptic remodeling, such as olfactory bulb and retina where its levels remain relatively high and are not down regulated (Tucker and Matus, 1988; Safaei and Fischer, 1989). MAPlB cDNA clones were isolated from expression libraries prepared from mouse (Lewis et al., 1986) and rat (Safaei and Fischer, 1989) brain mRNA of about 10 kb. The sequencing of the mouse MAPlB cDNA (Noble et al., 1989) deduces a 2464-aa protein (255 594 Da). In addition, the entire human MAPlB genomic region has been isolated, its organization has Correspondence to: Dr. I. Fischer, Department of Neurobiology and Anatomy, Medical College of Pennsylvania and Hahnemann University. 3200 Henry Avenue, Philadelphia, PA 19129, USA. Tel. ( 1-215) 842-4617; Fax (1-215) 843-9082; e-mail: Fischer@medcolpa.edu * On request, the authors will provide detailed experimental evidence for the conclusions reached in this Brief Note. Abbreviations: aa, amino acid(s); bp, base pair(s); cDNA, complemen- tary DNA; kb, kilobase or 1000 bp; MAPlB, microtubule-associated protein 1B; MAPIB, gene (DNA, RNA) encoding MAPlB; nt, nucleo- tide(s); tsp, transcription start point(s). SSDI 0378-1119(95)00061-3 been determined, and the complete coding region has been sequenced (Lien et al., 1994). In contrast, for rat MAPIB the available sequence is incomplete and lacks the 5’ end of the gene (Zauner et al., 1992). We cloned the 5’ end of MAPlB cDNA by RT-PCR amplification and used this clone to screen a rat genomic library. One 5’ primer (5’-AGAGGAACACTTCTCT- CAGGCTTG) and two 3’ primers (5’-CACCAG- CAAGTAGAACTTGCTGTC and 5’-TGAGCTCGC- CAGTGTTCTCAAAGC) derived from the mouse MAPlB cDNA (Noble et al., 1989) were used to amplify the corresponding region of the rat MAP1 B mRNA. Two cDNA products of 162 bp and 490 bp, respectively, were amplified, subcloned into pCR II vector (Invitrogene, San Diego, CA) and sequenced. Sequence analysis demon- strated that this region is more than 90% homologous with its mouse counterpart, confirming that these clones are the authentic cDNA clones of rat MAPIB. A hDASHI1 genomic DNA library prepared from Sprague Dawley male rat testis (Stratagene, La Jolla, CA) was screened using the 490-bp cDNA clone as a probe. Over 500 000 independent clones were screened, from which 12 positive clones were isolated. Phage DNA prepared from these clones was digested with different restriction enzymes, and analyzed by Southern blot hybridization