Books and Chapters of Books 
Leung, K.Y., Rosenshine, I., Garcia-del Portillo, F., 
and Finlay, B.B. 1992. Salmonella interactions 
with host cells. In Typhoid Fever: Strategies for 
the 90' s. Selected Papers from the First Asia- 
Pacific Symposium on Typhoid Fever (Pang, T., 
Koh, C.L., and Puthucheary, S.D., Eds.). Singa- 
pore: World Scientific, pp 135-139. 
Article 
Finlay, B.B., Rosenshine, I., Donnenberg, M.S., and 
Kaper, J.B. 1992. Cytoskeletal composition of at- 
taching and effacing lesions associated with en- 
teropathogenic Escherichia coli adherence to 
HeLa cells. Infect Immun 60:2541-2543. 
FUNDAMENTAL MECHANISMS IN TRANSCRIPTIONAL REGULATION 
Jack F. Greenblatt, Ph.D., International Research Scholar 
Initiation and termination of transcription are the 
principal fundamental processes whose regulation 
leads to control of gene expression in all cells. Dr. 
Greenblatt's objective is to characterize the enzy- 
mology of these processes and to understand how 
particular regulatory mechanisms act upon them. 
Because basic processes are often remarkably con- 
served among living organisms, these studies are 
carried out in both prokaryotes and eukaryotes. The 
study of transcription termination focuses on the 
bacterium Escherichia coli and its temperate bacte- 
riophage X, while studies on transcriptional initia- 
tion are performed with human cells. 
Transcriptional Antitermination 
by the N Protein of Phage X 
Each early operon of phage X contains multiple 
transcriptional terminators. The phage N protein 
prevents termination at all these terminators and 
thereby allows the expression of genes that are es- 
sential for the growth of the phage. Each early X 
operon is a target for N action because it contains an 
N utilization site (wM^site). Antitermination by N is 
assisted by the four host E. coli factors NusA, NusB, 
NusG, and ribosomal protein SIO. 
A major recent objective of the Greenblatt labora- 
tory was the reconstitution of antitermination by N 
in vitro in reactions containing only seven purified 
proteins. This objective was accomplished with the 
identification and purification of NusG, a protein 
encoded by an E. coli gene in which the nusG4 
mutation suppresses the effect of the nusAl muta- 
tion on antitermination by N. NusG was shown to 
interact directly with RNA polymerase and to travel 
together with N, NusA, NusB, and SI 0 on the surface 
of RNA polymerase in N-modified transcription 
complexes. It was also shown that the nut site is 
made of RNA and is assembled together with N and 
the Nus factors into a ribonucleoprotein particle on 
the surface of RNA polymerase. Antitermination at a 
terminator located just downstream from a nut site 
requires only an unstable complex containing N and 
NusA, but processive antitermination that persists 
for kilobases of DNA additionally requires NusB, 
NusG, and SIO. 
Two of the host factors, NusB and SIO, were 
shown to form a heterodimer that associates with 
RNA polymerase through ribosomal protein SIO. As 
well, the NusB-SlO complex was found to bind di- 
rectly to the boxA antiterminator element in E. coli 
ribosomal RNA {rrn) operons. This boxA element 
found in rrn operons is closely related to the boxA 
component of a X nut site. The nut site boxA ele- 
ment behaves as a mutated evolutionary descendant 
of the rrn operon boxA element, which cannot, by 
itself, bind NusB and SIO in the absence of a boxB 
element that, in turn, cooperatively binds N and 
NusA. In collaboration with the laboratory of 
Dr. Catherine Squires (Columbia University), Dr. 
Greenblatt's laboratory has established an in vitro 
system to study antitermination in the ribosomal 
RNA system and has shown that antitermination in 
this system also depends on NusB. 
NusG affinity chromatography was used to show 
that NusG interacts with the termination factor Rho. 
In the absence of N, this interaction facilitates termi- 
nation by Rho in vitro, but it is also important for 
antitermination by N. Dr. Greenblatt has proposed 
that the NusG molecule in an N-modified transcrip- 
tion complex sequesters Rho factor as it approaches 
the transcription bubble before Rho can interact 
with RNA polymerase and terminate transcription. 
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