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RESEARCH INTERESTS
Molecular Genetics; Regulation of transcription in prokaryotes
Bacteriopage Lambda's N protein as transcription antiterminator
Specifictiy in the macromolecular interactions among proteins
Specificity in the macromolecular interactions between proteins and their RNA targets
PUBLICATIONS
Bacteriophage lambda provides continuingly evolving grounds for molecular biological research. A particular line of interest has been a mode of transcription regulation peculiar to lambda and its many relatives1. Transcription of the three major 'developmental' operons of lambdoid bacteriophages is subject to termination at frequent DNA-coded stop-transcription signals. These barriers must be overcome for genome transcription to be completed, providing a full life cycle. Examination of different lambdoid phages in different laboratories has revealed a wealth of variety in the molecular solutions to 'anti-termination' of transcription.
In phages lambda, P22 and 21, a phage-coded "N" protein of about 100 amino acids interacts with 15-20-nucleotide "nut" sequences in the phage's RNA transcript. The sequences of the N proteins and nut RNAs are peculiar to each phage, however, giving individual molecular specificity to each interaction2. By cloning these particular sequences into bacterial plasmids, we make the N and nut molecules accessible to genetic manipulation and mutation, allowing the details of the specific interactions to be delved3,4. In other laboratories, structural-biochemical studies have validated the genetic evidence, and show molecular details of the reconfiguration of protein and RNA involved in the N-nut interaction. Closely related interactions are now known to activate transcription of the HIV virus and its relatives, making molecular intervention designable against those viruses.
The N-nut complex creates a nub for the addition of other proteins, such as NusA, coded by the Escherichia coli host of lambdoid phages, and finally engaging E. coli's RNA polymerase itself. Different segments of the small N proteins can be distinguished by their interactions with particular elements of this complex. Creating chimeric N proteins by joining segments from N proteins of lambda and P22, we now see that the functional segments of these two proteins do not align5. Thus these small proteins have evolved highly diversified sequences as well as internal rearrangements, although maintaining their location in the phage chromosome and their crucial role in lambdoid phage development. Lots of pressure to diversify, over long eons.
Selected Publications
1. Franklin, N.C. (1974) Altered reading of genetic signals fused to the N operon of bacteriophage lambda: Genetic evidence for modification of polymerase by N protein. J. Mol. Biol. 89:33-48.
2. Franklin, N.C. (1985) Conservation of genome form but not sequence in the transcription antitermination determinants of bacteriophages lambda, Ø 21 and P22. Mol. Biol. 181:75-84.
3. Doelling, J.H. and N.C. Franklin (1989) Effects of all single base substitutions in the loop of boxB on antitermination of transcription by bacteriophage lambda's N protein. Nucleic Acids Res. 17:5565-5577.
4. Franklin, N.C. (1993). Clustered arginine residues of bacteriophage λ N protein are essential to antitermination of transcription, but their locale cannot compensate for boxB loop defects. J. Mol. Biol. 231: 343-360.
5. Franklin, N.C. Chimaeras used to identify functional domains within the N antitermination proteins of lambda and P22. (In preparation, 2001).
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