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Apparent Average Length of the Transcriptional Unit in Bacteria¹

^a Department of Chemistry and Institute of Molecular Biology, University of California, Los Angeles, California 90024

ABSTRACT

The kinetics of radioactive phosphate incorporation into the adenosine and guanosine nucleoside triphosphate termini of bacterial ribonucleic acid (RNA) was studied. Knowledge obtained in a previous investigation of the kinetics of phosphate incorporation into their precursors, adenosine 5'-triphosphate and guanosine 5'-triphosphate, allowed calculation of the average half-lives of these termini, which were found to be approximately 170 s at 21.5 C for both. The ratio between the number of nucleotides incorporated into the interior of RNA chains per second and the number of termini synthesized per second was calculated by several methods and found to be between 4,000 and 8,000. Assuming that the initiation of synthesis of a RNA chain by deoxyribonucleic acid-dependent RNA polymerase always produces a triphosphate termini and that some termini do not have half-lives so short as to not be seen in this study (less than 10 s), this is the apparent average length of the transcriptional unit. The implication of these findings to the genetic organization of transfer RNA genes is discussed.

² Present address: Department of Molecular Biology, University of California, Berkeley, Calif. 94720.

¹ Publication no. 3198 from the Department of Chemistry, University of California at Los Angeles.