Molecular cloning and restriction enzyme analysis of a long repetitive DNA sequence in rice.

Rice long repetitive DNA (9-20 kbp) reassociating at Cot 50 M.s was cloned in pBR325. Out of several recombinants (Camr Ampr Tets), only a few were selected randomly for further characterization. The insert size in all these clones was 3-4 kbp. Restriction enzyme analysis showed the absence of EcoRI and BclI sites, presence of a single PstI and PvuII site and multiple sites for AluI in 3 clones namely pRLl, pRL7 and pRL10. The BamHI-PstI fragment of about 0·4 kbp in the pRL7 insert DNA (pRL7-0·4 kbp) was subcloned in M13mpl8 and partially sequenced using Sanger’s dideoxynucleotide chain termination method. Dot matrix comparison of this sequence with rice rDNA sequences revealed low homology with the 25S rDNA sequence of rice, however, hybridisation did not indicate any homology.