Cloning and characterization of cDNA copies of the 7S RNAs of HeLa cells

We have cloned cDNA copies of in vitro adenylated 7S RNA of HeLa cells. The most representative clones in the library contain DNA fragments copied from the 7SL and 7SK small RNAs. The two classes of recombinants share no homology. The 7SL RNA contains at the 5' end of the molecule sequences homologous to the Alu sequence family. Hybridization to human genomic DNA shows that the 7SL and 7SK clones are homologous to two different families of repetitive sequences.     

Human 7SL RNA consists of a 140 nucleotide middle-repetitive sequence inserted in an alu sequence

We have cloned and sequenced a cDNA copy of in vitro-polyadenylated 7SL RNA of HeLa cells. The cloned fragment is 303 bp long and has a composite structure. A central block of 140 bp is homologous to a new set of human middle-repetitive sequences. This block appears to be inserted in an Alu consensus sequence, 100 bp from the 5' end and 40 bp from the 3' end of the Alu monomer. Two 6 bp direct repeats are found at the junction between the Alu flanking sequences and the central element. The analysis of several clones shows the existence of sequence microheterogeneity in the 5' portion of the molecule. The 7L DNA probably represents a subset of the Alu family of DNA, highly conserved in evolution.