Question 4 Lambda phage is a virus that infects E coli bacteria. After infecting the bacteria it can take one of two paths, lysis or lysogeny. In the lysis path, the phage makes many copies of itself, breaks out of the cell and infects new cells. In lysogeny, the phage incorporates its DNA into the bacterial dna and lays dormant in the cell. The presence of a protein called lambda repressor influences which path is taken by inhibiting lysis. When lambda repressor is present it turns off or represses the genes that allow the virus to reproduce, thus no phage progeny are produced and no cell lysis occurs a)In studying this protein you find that lambda repressor binds DNA at a site that overlaps he promoter for the lysis genes. Propose a mechanism for repression based on this information The mechanisim for repression would be analogous to that of the lac operon. When lamba repressor binds, it prevents transcription of the genes required to complete the lysis steps of phage replication b)Activators typically work by binding near a promoter site and recruiting RNa polymerase to the promoter by forming non-covalent bonds with it. This helps the polymerase attach to the promoter and increases transcription from that promoter Although Lambda repressor turns off the transcription of the lysis genes, it stimulates the expression of its own lambda repressor gene(acts as an activator). In studying lambda pressor you find that there are two amino acids, Asp and Glu, which are essential to the activator function Based on this information what type of bonds do you expect Lambda repressor to make with Rna polymerase and what type of amino acids do you expect to find on polymerase participating in these bonds? g ght expect the Lambda repressor protein to form ionic bonds wvith the RNA polymerse ld predict that positively charged amino acids such as lys, arg, and his would be found on the ploymerase participating in these bond 7012Fall2003Question 4 Lambda phage is a virus that infects E. coli bacteria. After infecting the bacteria it can take one of two paths, lysis or lysogeny. In the lysis path, the phage makes many copies of itself, breaks out of the cell and infects new cells. In lysogeny, the phage incorporates its DNA into the bacterial DNA and lays dormant in the cell. The presence of a protein called lambda repressor influences which path is taken by inhibiting lysis. When lambda repressor is present it turns off or represses the genes that allow the virus to reproduce, thus no phage progeny are produced and no cell lysis occurs. a) In studying this protein you find that lambda repressor binds DNA at a site that overlaps the promoter for the lysis genes. Propose a mechanism for repression based on this information. The mechanism for repression would be analogous to that of the lac operon. When lamba repressor binds, it prevents transcription of the genes required to complete the lysis steps of phage replication. b) Activators typically work by binding near a promoter site and recruiting RNA polymerase to the promoter by forming non-covalent bonds with it. This helps the polymerase attach to the promoter and increases transcription from that promoter. Although Lambda repressor turns off the transcription of the lysis genes, it stimulates the expression of its own lambda repressor gene (acts as an activator). In studying lambda repressor you find that there are two amino acids, Asp and Glu, which are essential to the activator function. Based on this information what type of bonds do you expect Lambda repressor to make with RNA polymerase and what type of amino acids do you expect to find on polymerase participating in these bonds? You might expect the Lambda repressor protein to form ionic bonds with the RNA polymerse. You could predict that positively charged amino acids such as lys, arg, and his would be found on the ploymerase participating in these bonds. 7.012 Fall 2003 4