Gene, 17(1982)263-270 Elsevier Biomedical Press 263 Sequence organization of a viral DNA insertionpresent in the zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQP adenovirus-type-Sransformed hamster line BHK268-C31 (Recombinant DNA; electron microscopy; restriction enzyme mapping; X Charon 4A phage vector) G. Westin *, L. Visser **, J. Zabielski *, A.D.M. van Mansfeld **, U. Pettersson * and Th. H. Rozijn ** * Department of Microbiology, The Biomedical Centre, Box 581, S-751 23 Uppsala (Sweden), and ** Laboratory for Physiological Chemistry, State University of Utrecht, 3521 GG Utrecht (The Netherlands) (Received September 14th, 1981) (Accepted December 10th. 1981) SUMMARY The hamster cell line BHK268-C31 contains two large viral inserts which both include sequences from the left-hand end of adenovirus type5 (Ad5) DNA. One of these viral inserts has been cloned in the X vector Charon 4A. Electron microscopic analysis and restriction enzyme mapping shows that the recombi- nant carries a 4.4-kb-long colinear segment of viral DNA, which is located between map positions 1.5 and 14.2 in the Ad5 genome. The junctions between viral DNA and flanking sequences have been sequenced and found not to show any specific features. One of the junctions is located in the Ela coding region, 573 bp from the left-hand end of the Ad5 genome, whereas the other junction is situated in the coding region for polypeptide lVa2. The promoter region as well as the cap site for the mRNAs from region Ela are thus missing from this insert and its role in viral transformation is unclear. INTRODUCTION Transformation of rodent cells by adenovirus involves integration of viral DNA into the genome of the host cell. The left-hand early region (region El) persists in all fully transformed cells and its expression is necessary for initiation and mainte- nance of transformation (Gallimore et al., 1974; * Reprint requests should be addressed to Dr. G. Westin. Abbreviations: Ad5. adenovirus type 5; bp, base pairs; kb, kilobase pairs; SSC, 0.15 M NaCl, 0.015 M Na,.citrate, pH 1.6. Graham et al., 1974; 1978). Integration patterns of adenovirus sequences have been studied by several groups in a large number of cell lines, mainly by the Southern blotting technique (Sutter et al., 1978; Visser et al., 1980; Doerfler et al., 1980; Sambrook et al., 1980; Dorsch-Hasler et al., 1980). It appears that integrated viral sequences occur at multiple sites in the cellular genome, each transformed cell line exhibiting its own characteristic integration pattern. Furthermore, variable segments of the adenovirus genome are found to be present in these cell lines. Available results seem to imply that the site of adenovirus integration in the cellu- 0378-l 119/82/0000-0000/$02.75 0 1982 Elsevier Biomedical Press