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A combination of DNA hybridization analyses and tissue sectioning techniques demonstrate that ras gene mutations occur in over a third of human colorectal cancers, that most of the mutations are at codon 12 of the c-Ki-ras gene and that the mutations usually precede the development of malignancy.

Here we report the isolation of a cDNA encoding a new p53‐associating protein. This new protein has been called MDMX on the basis of its structural similarity to MDM2, which is especially notable in the p53‐binding domain. In addition, the putative metal binding domains in the C‐terminal part of MDM2 are completely conserved in MDMX. The middle part of the MDMX and MDM2 proteins shows a low degree of conservation. We can show by co‐immunoprecipitation that the MDMX protein interacts specifically with p53 in vivo. This interaction probably occurs with the N‐terminal part of p53, because the activity of the transcription activation domain of p53 was inhibited by co‐transfection of MDMX. Northern blotting showed that MDMX, like MDM2, is expressed in all tissues tested, and that several mRNAs for MDMX can be detected. Interestingly, the level of MDMX mRNA is unchanged after UV irradiation, in contrast to MDM2 transcription. This observation suggests that MDMX may be a differently regulated modifier of p53 activity in comparison with MDM2. Our study indicates that at least one additional member of the MDM protein family exists which can modulate p53 function.

Currently, the preferred host for the production of early region-1 (E1)-deleted recombinant adenoviruses (rAdV) is cell line 293, which was generated by transformation of human embryonic kidney cells by sheared adenovirus 5 (Ad5) DNA. To develop alternative hosts for the production of rAdV, we generated adenovirus-transformed human cell lines by transformation of human embryonic retinoblasts (HER) with a plasmid containing base pairs 79-5789 of the Ad5 genome. One of the established HER cell lines, which we called 911, exhibited favorable growth characteristics and was chosen for further study. This cell line is demonstrated to have several characteristics in common with the well-known 293 cell line: The 911 cell line is highly transfectable, and exhibits similar frequencies of homologous recombination. However, it has additional characteristics that make it a useful alternative for 293. The 911 cells perform particularly well in plaque assays. Upon infection with E1-deleted adenoviruses, plaques become apparent in monolayers of 911 cells already after 3-4 days versus 4-10 days in monolayers of 293 cells, thereby reducing the time required for quantitative plaque assays. Furthermore, yields of E1-deleted adenovirus vectors up to three times as high as those achieved with 293 cells can be obtained with 911 cells. Finally, the Ad5-DNA content of the 911 cell line is completely known. These features make the 911 cell line a useful alternative for the construction, propagation, and titration of E1-deleted recombinant adenoviruses.

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