being introduced into the zinc finger domain to ad- 
dress this issue. 
ElA appears to bind directly to YYl to modulate 
its activity. When ElA and YYl proteins are mixed, 
they form a complex that can be detected by sedi- 
mentation in a sucrose gradient. The sedimentation 
coefficient of the complex suggests that it is a 
heterodimer. An El A- YYl interaction can also be 
detected when [^^PJ-iabeled ElA protein is used to 
probe a protein blot in which YYl protein has been 
subjected to electrophoresis and transferred to a ni- 
trocellulose membrane. This experiment argues 
that the interaction is direct, because both proteins 
were produced in bacterial cells, eliminating the 
possibility that an additional eukaryotic protein was 
present and serving to bridge between E 1 A and YYl . 
Segments of the YYl protein were tested for their 
ability to interact with the ElA protein. The ElA- 
YYl interaction maps to the central third of the YYl 
protein, at a site distinct from the carboxyl-terminal 
repression domain. Experiments are in progress to 
search for cellular proteins that might bind to YYl 
within its repression and ElA interaction domains. 
Role for an Adenovirus E4 Protein 
in Rat Mammary Oncogenesis 
All adenoviruses that have been tested are able to 
transform established rodent cell lines oncogeni- 
cally, and some adenoviruses can induce sarcoma- 
tous tumors at the site of inoculation into rodents. 
Ad9 appears to be unique among the adenoviruses 
in that it induces exclusively estrogen-dependent 
mammary tumors in female rats. These tumors in- 
clude mammary fibroadenomas, which are common 
benign breast tumors of women, as well as phyllode- 
like tumors and sarcomas. 
Examination of the viral genes expressed in a vari- 
ety of Ad9-induced rat mammary tumors revealed 
that ElAbut not ElB mRNAwas present. The tumors 
also all contained mRNAs encoded by the Ad9 E4 
gene. This was in contrast to sarcomas induced by 
other adenovirus serotypes that invariably contain 
mRNAs encoded by both ElA and ElB oncogenes 
but only occasionally express E4 mRNAs. 
By constructing recombinant viruses between 
Ad9 and Ad26 (a related adenovirus that does not 
induce mammary tumors) , it was possible to demon- 
strate that the Ad9 E4 gene is required to produce 
mammary tumors. This gene is also able to induce 
the formation of transformed foci in an established 
rat cell line, suggesting it plays a direct role in onco- 
genesis. This demonstrates for the first time that an 
adenovirus gene outside of the classic ElA/E IB- 
transforming region can influence in vivo oncogen- 
esis. Work is in progress to identify the specific Ad9 
E4 protein involved {E4 encodes at least six poly- 
peptides) and to elucidate the mechanism by which 
it contributes to mammary oncogenesis. (This proj- 
ect was supported by grants from the National 
Cancer Institute, National Institutes of Health.) 
Dr. Shenk is also James A. Elkins, Jr., Professor 
of Molecular Biology at Princeton University and 
Adjunct Professor of Biochemistry at the Univer- 
sity of Medicine and Dentistry of New Jersey, Rob- 
ert Wood Johnson Medical School. 
Articles 
Kleinberger, T., and Shenk, T. 1991. A protein 
kinase is present in a complex with adenovirus 
ElAproteins. Proc Natl Acad Sci USA 88:1 1 143- 
11147. 
Parks, C.L., Chang, L.-S., and Shenk, T. 1991. A 
polymerase chain reaction mediated by a single 
primer: cloning of genomic sequences adjacent to 
a serotonin receptor protein coding region. Nu- 
cleic Acids Res 19:7155-7160. 
Seto, E., Shi, Y., and Shenk, T. 1991. YYl is an 
initiator sequence-binding protein that directs 
and activates transcription in vitro. Nature 
354:241-245. 
Shi, v., Seto, E., Chang, L.-S., and Shenk, T. 1991. 
Transcriptional repression by YYl, a human GLI- 
Kriippel-related protein, and relief of repression 
by adenovirus ElA protein. Cell 67:377-388. 
Takagaki, Y., MacDonald, C.C., Shenk, T., and Man- 
ley, J.L. 1992. The human 64-kDa polyadenyla- 
tion factor contains a ribonucleoprotein-type RNA 
binding domain and unusual auxiliary motifs. 
Proc Natl Acad Sci USA 89:1403-1407. 
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