experiments indicate that affinity of peptides R and L for the DNA fragment containing the 3'-flanking region of the gene was greater than for the fragment containing the 5'-flanking region. The results thus demonstrate specific interaction of peptides R and L with regulatory sequences of the IL 2 gene. The negative or positive character of regulation of IL 2 production by T lymphocytes may evidently be due to complex formation between specific nucleotide sequences of the IL 2 gene and the above-mentioned peptides. So far there has been only one indication in the literature of the existence of a protein nuclear factor AP-I [3], capable of regulating expression of the inducible IL 2 gene through interaction with its sequences. It is probable that peptide factors R and L may give an independent; regulatory effect, whereas peptide SKD may act indirectly through other protein factors. LITERATURE CITED . . 3. 4. 5. O. S. Merimskaya, A. V. Pronin, and T. N. Kuzina, Preparation and Testing of IL 2 for Experimental Purposes. Technical Recommendations [in Russian], Moscow (1986). G. I. Chipens, R. E. Vegner, N. G. Ieveenya, et al., Izv. Akad. Nauk Latv. SSR, No. 9, 85 (1986). P. Angel, M. Imagawa, R. Chin, et al., Cell, 49, No. 6, 729 (1987). S. L. Berent and J. C. Seval, Biochemistry, 23, 2977 (1984). J. M. Wright, P. A. Wiersma, and G. H. Dihon, Eur. J. Biochem., 168, No. 1,281 (1987). NEW HOST DNA SPECIFICITY SYSTEMS PAE 610 AND PAE 603 M. I. Tediashvili, T. V. Goryan, T. D. Koberidze, T. G. Chanishvili, and I. I. Nikorskaya UDC 578.81:577.213.7 KEY WORDS: restriction; modification; bacteriophage; plasmids; cross titration The rapid development of genetic engineering has been largely due to the discovery and use of highly specific restriction endonucleases and modifying methylases, constituting the host specificity system (HSS) of DNA. Several hundreds of these enzymes are now known [13], but the broad front of research requires expansion of the arsenal of enzymes and identification of new restriction endonucleases and methylases. This task is linked, in turn, with the search for and study of new DNA restriction and modification (r-m) systems. The aim of this investigation was to discover HSS among strains of Pseudomonas aeruginosa and to study them. Identification of RM systems in these microorganisms in the proposed research, by contrast with systems described previ- ously [5, 9, 10, 11], is based on priority of biological testing, which enables a large number of strains to be tested and the distribution of HSS among microorganisms of a given species to be tested and, finally, the discovery of RM systems to be differentiated from the HSS already known. Institute of Biochemistry of Plants, Academy of Sciences of the Georgian SSR, Tbilisi. Institute of Biological and Medical Chemistry, Academy of Sciences of the USSR, Moscow. (Presented by Academician of the Academy of Medical Sciences of the USSR S. S. Debov.) Translated from Byulleten' l~ksperimental'noi Biologii i Meditsiny, Vol. 112, No. 7, pp. 91-94, July, 1991. Original article submitted May 28, 1990. 1026 0007-4888/91/000%1026512.50 o1991 Plenum Publishing Corporation