THE 2ND INTRON OF THE K-RAS GENE CONTAINS REGULATORY ELEMENTS ASSOCIATED WITH MOUSE LUNG-TUMOR SUSCEPTIBILITY

We have previously demonstrated the preferential activation of the K-r as gene from the susceptible A/J parent ire lung tumors from F-1 mouse hybrids. In the present study, the mechanism of this observation is f urther investigated. Higher levels of expression of A/J K ras allele w ere detected in lung adenomas (30 of 30) from the C3A mouse. In additi on, three K-ras alleles, designated as susceptible (K-s), intermediate (K-i), or resistant (K-r), were identified by sequence analysis of th e second intron of the K-ras gene from 32 strains of mice. These K-ras alleles are associated with differences in mouse lung tumor susceptib ility. All K-r alleles have a tandem 37-bp direct repeat (nt 282-355) in the second intron of the K-ras gene. K-s and K-i alleles have only one copy of the 37-bp sequence (nt 282-318). K-s strains have three ba se variations at nt 288, 296, and 494, and K-i strains have two base v ariations at nt 288 and 494 in the second intron of the K-ras gene. Di fferential protein-binding patterns were observed in gel-mobility-shif t experiments between the duplicated 37-bp sequence of the K-r allele and the single 37-bp sequence of the K-s and K-i alleles. DNase I foot printing assay revealed protein binding sites in the second intron of the K-ras gene that correspond to the tandem repeat sequences. Our dat a suggest that higher expression of the A/J allele relative to C3H all ele may be responsible for the allele-specific activation of the K-ras gene in lung tumors from F-1 hybrid mice.