The reciprocal chromosome translocation, t(8;14), involving the heavy chain locus on chromosome 14 and the c-myc oncogene on chromosome 8 is a characteristic of the B-cell malignancies Burkitt's lymphoma and acute lymphoblastic leukaemia (ALL). We have cloned and sequenced the t(8; 14) breakpoints of an African Burkitt's lymphoma cell line, P3HR-1, and a pre-B cell ALL cell line, 380. In each case the region of chromosome 8 involved has recombined with a JH region on chromosome 14. The two sites of breakage on chromosome 8 lie within 70 base pairs (bp) of one another. At each joining site, sequences homologous to the signal sequences thought to be recognized by the V-D-J recombinase were identified, as were N regions. In B-cell chronic lymphocytic leukaemias (B-CLL) carrying the t(11; 14) chromosome translocation and in follicular lymphomas carrying the t(14; 18) translocation, the V-D-J recombinase is implicated in the mechanism of chromosomal translocations. We speculate that the same enzymatic mechanism is responsible for the t(8; 14) translocations in African Burkitt's lymphoma and pre-B cell ALL.

We have cloned the translocation-associated and homologous normal MYC alleles from SKW-3, a leukemia T-cell line with the t(8;14)(q24;qll) translocation, and determined the sequence ofthe MYC oncogene first exon and flanking 5' putative regulatory regions. S1 nuclease protection experiments ut g a MYC first exon probe demonstrated Hnscriptional deregulation of the MYC gene asated with the T-cell receptor a locus on the 8q + chromosome of SKW-3 cells. Nudeotide sequence analysis of the translocation-aociated (8q +) MYC allele identified a single base substitution within the upstream flanking region; the homologous nontranslocated allele contained an additional substitution and a two-base deletion. None of the deletions or substitutions localized to putative 5' regulatory regions. TheMYC first exon sequence was germ line in both alleles. These results demonstrate that alterations within the putative 5' MYC regulatory regions are not necessarily involved in MYC deregulation in T-cell leukemias, and they show that juxtaposition of the T-cell receptor a locus to a germ-line MYC oncogene results in MYC deregulation.

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Hereditary pancreatitis (HP) is the second most common cause of chronic childhood pancreatitis in the United States. Mutations in the cationic trypsinogen gene on chromosome 7 are known to cause HP. We identified four families in West Virginia with symptoms consistent with HP. To determine whether members of these families had defects in the trypsinogen gene, we tested for linkage between the HP gene and simple tandem repeat markers on chromosome 7q and screened for a specific mutation in the cationic trypsinogen gene. Two-point linkage analysis indicated that the disease gene is closely linked to three 7q markers (D7S661, D7S2511, and D7S1805). Restriction fragment length polymorphism analysis showed that all clinically affected members and nonpenetrant carriers from the four families carried a G to A mutation in the third exon of the trypsinogen gene. These findings indicate that this mutation is the cause of HP in the families in our study. The observation that most individuals who carry the mutation have symptoms of HP is consistent with the high but incomplete penetrance of the trait. The presence of a single mutation and a common linked haplotype indicates that the defective allele arose in an ancestor common to all four families.

Rtsl is a high-molecular-weight (126 x 106) plasmid encoding resistance to kanamycin. It expresses unusual temperature-sensitive phenotypes, which affect plasmid maintenance and replication, as well as host cell growth. We have cloned the essential replication region of Rtsl from pAK8, a smaller derivative which is phenotypically similar to Rtsl. Restriction endonuclease digests of isolated pAK8 deoxyribonucleic acid were allowed to "self-ligate" (ligation without an additional cloning vector) and subsequently were used to transform Escherichia coli strain 20S0 to kanamycin resistance. Screening of these strains for the phenotypes of thermosensitive host growth and temperature-dependent plasmid elimination demonstrated that these two properties were expressed independently. Furthermore, it was shown that the Rtsl replication locus per se is not necessarily responsible for altered host growth at the nonpermissive temperature. The kanamycin resistance fragment of pAK8 was also cloned into pBR322. Electrophoretic analysis of BamHI restriction enzyme digests of this plasmid and similar digests of an Rtsl miniplasmid has allowed the identification of an 18.6-megadalton fragment carrying the replication locus and a 14.1-megadalton fragment carrying the kanamycin resistance gene. Rtsl is a high-molecular-weight R factor of the T-incompatibility group (4) which confers upon its host resistance to kanamycin. When examined in Escherichia coli 20S0, the Rtsl plasmid copy number is stringently regulated (10), and the molecular size is approximately 126 megadaltons (Mdal) (10, 11). The unique feature of Rtsl is the thermosensitivity of strains harboring this plasmid during incubation at 42.5°C. At 42.5°C, the efficiency of conjugal transfer is markedly diminished (30), and the Rtsl-mediated resistance to T-even bacteriophages is not expressed (12, 17, 36). In addition, there is a detrimental effect on the growth of cells carrying Rtsl (27, 35), and significant membrane lesions have been observed (12). Furthermore, an alteration occurs in the control of autonomous maintenance, causing the subsequent appearance of Rsegregants (11). The ability of Rtsl DNA to replicate as a closed covalent circle (CCC) is impaired at 42.50C (11, 33), which may correlate with the effect of Rtsl on host growth at the nonpermissive temperature. Recently, two groups have selected strains