Analysis of the structure of DNA cistrons coding proteins with known sequences]

Proceeding from the amino acid sequence of a number of proteins, with the help of a special computer program we have determined the frequency of pyrimidine isopliths of different length, the degree of clustering and the degree of asymmetry of complementary chains of the corresponding DNA cistrons, as well as the range of variation of these parametres which depends on the code degeneracy. The degree of asymmetry of the chains of DNA cistrons (H/L), calculated for 255 proteins of a known composition, may vary from 0.7 to 1.8. For 90% of these proteins the mean Py/Pu ratio in the coding chain of DNA is above 1. The conclusion has been made that the majority of amino acids contained in the proteins is coded for by purine triplets. It was found that the distribution of pyrimidine isopliths between DNA cistrons coding for different proteins is other than random and has a "DNA-like" character. The degree of clustering of pyrimidines (beta) in cistrons of different proteins may vary from 6.0 to 14.3. The cistrons of some proteins were found to contain long lyrimidine fragments with about 24 residues. A positive correlation (r2 = 0.74) was found to exist between the degree of clustering of pyrimidines and the degree of asymmetry of the chains corresponding to different proteins of DNA cistrons.     

Cloning and genetic analysis of tra cistrons of the Tra 2/Tra 3 region of plasmid RP1

Transfer-defective mutants of the 10.4-kb Tra 2/Tra 3 region of RP1 were identified by their ability to be complemented by clones carrying all or part of this region. The respective mutations occurred in six cistrons whose order (traA, B, E, R, P, Q) and location were determined by deletion and insertion mapping. The cistrons occupy a minimum of 5.5 kb with the most distal, traA, spanning the 28.0-kb map position and traR the KpnI site at map position 24.1 kb. Each cistron is expressed independently, as Tn5 or Tn504 insertions in any one cistron do not affect the other five. The phenotypes controlled by each cistron suggest that all contribute to pilus biosynthesis/function while three (traB, R, and P) also contribute to surface exclusion. Given the occurrence of tra cistrons in the "silent" region between Tra 2 and Tra 3 we propose that the epithet "Tra 2" should be used to describe this entire region.