Cloned complementary deoxyribonucleic acid of Drosophila cells. Relationship of genome copy number to messenger ribonucleic acid abundance.

Recombinant DNA plasmids containing DNA sequence complementary to poly(adenylic acid) [(poly(A)] containing RNA from the cytoplasm of Drosophila Kc tissue culture cells were constructed. The reiteration frequency in the genome of the RNA homologous to the 20 randomly selected clones was determined by two rapid methods. Of the 20, 17 were determined to be single copy, 2 were repeated several (2-4) times, and 1 was repeated approximately 10 times. The steady-state level of mRNAs homologous to the 20 cDNAs was quantitated and varied more than 160-fold. The RNAs ranged from 0.16% to less than 0.001% of the poly(A)-containing RNA.