We have characterized the interaction between selected novel RNA-binding peptides and their target RNA. The RNA is comprised of two elements, a GCAA tetraloop, a member of the thermodynamically stable GNRA-type (where N is A or G, U, C; R is G or A) tetraloops, and a tri-purine bulge found in the frameshift stimutating structure on the human immunodeficiency virus type 1 (HIV-1) gag-pol mRNA. Peptides that bind specifically to the target RNA were selected from a combinatorial library based on arginine-rich motif (ARM) by a bacterial reporter system. We performed mutational studies using the reporter system and gel shift assays and found that the binding affinity and specificity of the RNA were mainly dependent on the GNRA-type tetraloop, and a modest contribution was also attributed to the bulge structure. Our finding reveals a novel mode of interaction by an RNA-peptide complex and expands our knowledge on the diversity of molecular recognition.
SummaryIn bacteriophage l, formation of a transcriptional anti-termination complex involving the elongating RNA polymerase is mediated by the interaction of boxB RNA with the RNA-binding domain of the N protein (N peptide). In an attempt to understand the spatial requirements for boxB/N peptide interaction within the anti-termination complex, the effects of changes in the distance between boxA and boxB RNA, the length of the boxB stem, and the distance between the N peptide and remainder of the N protein were examined using a bacterial reporter system. It was found that the requirements for boxB stem length and the distance between N peptide and the remainder of N were optimized and strict. In contrast, replacement of the boxB/N interaction by heterologous RNA-peptide interactions appeared to relax the strict requirement for RNA stem length and the orientation of the RNA-binding peptide, presumably due to the absence of the cooperative interaction between boxB/N and the host factor NusA. In addition, the decrease in activity upon stem lengthening could be partially suppressed by simultaneous lengthening of the RNA spacer. A further understanding of the structural organization of the anti-termination complex may provide insights into how functional ribonucleoprotein complexes may be engineered.
In bacteriophage lambda, formation of a transcriptional antitermination complex consisting of the lambda N protein, nut RNA transcript (boxA-boxB), host factors, and RNA polymerase is mediated by the interaction of the boxB RNA with the RNA-binding domain of N. In order to understand the spacial requirements of this boxB/N interaction within the complex, the effects of changes in the length of the nut site linker, the boxB stem, and the peptide spacer connecting the RNA-binding domain and activation domain of N were examined using a bacterial reporter system. As a result, we found that the requirements for the boxB stem length and N peptide linker length were optimized and strict. In contrast, when the boxB/N interaction was replaced by heterologous RNA/peptide interactions, the strict requirement for the length of the peptide linker and the RNA stem was relaxed, presumably due to the absence of the interaction between boxB/N and the host factor NusA in the wild-type complex. It was also shown that the decrease in activity upon stem lengthening could be partially suppressed by simultaneous lengthening of the RNA spacer, suggesting that a further understanding of the organization of the antitermination complex may provide insights into the engineering of functional ribonucleoprotein complexes.
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