Sk. Chatterjee et al., ANALYSIS OF THE SEQUENCES OF HUMAN BETA-1,4-GALACTOSYLTRANSFERASE CDNA CLONES, International journal of biochemistry & cell biology, 27(3), 1995, pp. 329-336
UDP-galactose:beta-1,4 N-acetyl glucosamine galactosyltransferase (4 b
eta GT) is a promising tumor marker for ovarian cancer. To study the r
ole of 4 beta GT in malignant transformation at the molecular level hu
man 4 beta GT cDNA and genomic clones were isolated and analyzed. For
the isolation of 4 beta GT cDNA and genomic clones, a human fetal live
r cDNA library in lambda gt11 and a human genomic library in EMBL-3B v
ectors respectively were screened using a 4 beta GT cDNA insert as the
probe. Complete sequence of the cDNA clones were determined by subclo
ning in plasmid vectors, and compared with the published sequence of h
uman liver 4 beta GT. Presence of various 4 beta GT exons in the genom
ic clones were determined by Southern blot analysis using specific oli
godeoxynucleotide probes. Among the 5 cDNA clones isolated, 2 clones G
TN 6 and GTN 17 were sibling clones and had a nucleotide sequence iden
tical to the published 4 beta GT cDNA sequence, except at the 3'-end,
where these clones had 7 unique nucleotide sequences. One cDNA clone,
GTN2 also had a nucleotide sequence identical to that of 4 beta GT, ex
cept for 3 G residues at the 5'-end. One cDNA clone, GTN 1, had a uniq
ue sequence at the 5'-end comprising of 74 nucleotides. Another clone,
GTN 20, was unrelated to 4 beta GT. Analysis of genomic clones showed
that 4 beta GT exons 3, 4, 5 and 6 were present in a 14 kb genomic cl
one, EMGT-4. Exon 1 was present in a separate 16 kb clone, EMGT-6. No
clone was detected for exon 2. Southern blot analysis and partial rest
riction mapping of EMGT-6 showed that the 74 nucleotide unique sequenc
e of GTN1 was present in this genomic clone. But this DNA fragment has
separated from exon 1 by a distance of about 10 kb. This study showed
that human 4 beta GT cDNA had divergent sequences, both at the 5'- an
d 3'-ends. Among them, a 74 nucleotide unique sequence at the 5'-end o
f GTN1 is present along with exon 1 in a genomic clone. It is proposed
that the divergent cDNA clones represent various isoenzymes of 4 beta
GT found in normal and malignant cells.