Earlier studies from our laboratory have demonstrated the expression of mRNA for GC-A in human retina by using RT-PCR. The PCR product (700bp) obtained from the reverse transcribed poly A+ fractions of human retina (using oligonucleotide primers designed from the human placental GC-A cDNA sequence) was used in the present study as a hybridization probe to clone the GC-A from a human retinal library. Two clones hybridizing with a radiolabeled probe were isolated and subjected to subsequent screenings. A clone isolated from one of the original clones was grown, the phage DNA purified by cesium chloride gradient and the size of the insert (1.2 kb) was determined by EcoR1 digestion and by PCR amplification using amplimers. Partial sequences obtained both from the phage DNA and from the amplimer amplified PCR product were found to be the same. The 1.2 kb insert was rescued into bluescript and the sequence of the insert was determined. Comparison of the cloned insert sequence with the sequence of the human placental GC-A did not show the expected similarity. It is possible this clone does not represent GC-A and it was picked up as a false positive clone during the screening of cDNA library. The final sequence analysis of the other original clone is yet pending.
