Western Kentucky University
Analysis of RNA Mediated Antitermination in Erwinia tasmaniensis Bacteriophage φEt88
Institution
Western Kentucky University
Faculty Advisor/ Mentor
Rodney A. King
Abstract
RNA polymerase is a highly processive enzyme but transcripton terminators can block its progress. The ability to override termination signals has evolved as an effective mechanism to control gene expression. Processive antitermination occurs when an antiterminator element modifies RNA polymerase so that it resists termination at multiple downstream sites. This type of antitermination was first discovered in bacteriophage λ and is common in many lambdoid phages. In λ, early gene expression is achieved through the action of the RNA binding protein N and the RNA transcript of N-utilization sites (nut sites). The N-nut complex modifies RNA polymerase such that pausing and termination of transcription is suppressed. Not all antitermination mechanisms require protein factors. In RNA-mediated antitermination, the RNA transcript of polymerase-utilization sites, or put sites, directly convert RNA polymerase into a termination resistant form. This mechanism was first discovered in bacteriophage HK022. Bacteriophage phiEt88, which infects the bacterium Erwinia tasmaniensis, was discovered to have a putL and a putR site by sequence analysis. This is the first example of a bacteriophage that possesses put-like antiterminators but does not use E. coli as its host. Antitermination reporter fusions indicate that the putative put sites of phiEt88 promote efficient antitermination.
Analysis of RNA Mediated Antitermination in Erwinia tasmaniensis Bacteriophage φEt88
RNA polymerase is a highly processive enzyme but transcripton terminators can block its progress. The ability to override termination signals has evolved as an effective mechanism to control gene expression. Processive antitermination occurs when an antiterminator element modifies RNA polymerase so that it resists termination at multiple downstream sites. This type of antitermination was first discovered in bacteriophage λ and is common in many lambdoid phages. In λ, early gene expression is achieved through the action of the RNA binding protein N and the RNA transcript of N-utilization sites (nut sites). The N-nut complex modifies RNA polymerase such that pausing and termination of transcription is suppressed. Not all antitermination mechanisms require protein factors. In RNA-mediated antitermination, the RNA transcript of polymerase-utilization sites, or put sites, directly convert RNA polymerase into a termination resistant form. This mechanism was first discovered in bacteriophage HK022. Bacteriophage phiEt88, which infects the bacterium Erwinia tasmaniensis, was discovered to have a putL and a putR site by sequence analysis. This is the first example of a bacteriophage that possesses put-like antiterminators but does not use E. coli as its host. Antitermination reporter fusions indicate that the putative put sites of phiEt88 promote efficient antitermination.