On the cloning of eukaryotic total poly(A)-RNA populations in Escherichia coli

A total clone bank of cDNAs synthesized from mouse liver poly(A)-RNA was constructed in Escherichia coli K-12 RR1 using the plasmid pBR322. Sequences of cDNAs were inserted into the PST-I site of pBR322 by the "G-C-tailing" method. Bulk preparations of these cDNA sequences were obtained by treatment of the resultant total hybrid plasmid population with PST-I. Aliquots of this cDNA material were then labeled with 32P by "nick translation" using E. coli DNA polymerase I for the preparation of hybridization probes. Experiments involving the back-hybridization of these probes to the total hybrid-plasmid clone bank population revealed that virtually all of the liver poly(A)-RNA sequences were represented in the total clone bank. The long term stability of these sequences residing in RR1 host cells was then examined through extensive serial passage of the initial total clone cell population culture. The results showed: 1) that the small percentage of natural pBR322 molecules (containing no cDNA inserts) usually present in such total clone bank preparations do not outgrow the respectively hybrid specie of plasmids in these populations: 2) few, if any, cDNA sequences are completely lost; and 3) some redistribution of the abundant and more unique DNA sequences probably does occur. The use of total clone hybrid-plasmid populations (constructed from poly(A)-RNA isolated from different tissues) described here should allow the identification of tissue-specific RNA sequences through the use of cross-hybridizaton techniques.