ABSTRACT
Germline mutations in PMS2 are associated with Lynch syndrome (LS), the most common known cause of hereditary colorectal cancer. Mutation detection in PMS2 has been difficult due to the presence of several pseudogenes, but a custom-designed long-range PCR strategy now allows adequate mutation detection. Many mutations are unique. However, some mutations are observed repeatedly across individuals not known to be related due to the mutation being either recurrent, arising multiple times de novo at hot spots for mutations, or of founder origin, having occurred once in an ancestor. Previously, we observed 36 distinct mutations in a sample of 61 independently ascertained Caucasian probands of mixed European background with PMS2 mutations. Eleven of these mutations were detected in more than one individual not known to be related and of these, six were detected more than twice. These six mutations accounted for 31 (51%) ostensibly unrelated probands. Here, we performed genotyping and haplotype analysis in four mutations observed in multiple probands and found two (c.137G>T and exon 10 deletion) to be founder mutations and one (c.903G>T) a probable founder. One (c.1A>G) could not be evaluated for founder mutation status. We discuss possible explanations for the frequent occurrence of founder mutations in PMS2.
Subject(s)
Adenosine Triphosphatases/genetics , Colorectal Neoplasms, Hereditary Nonpolyposis/genetics , DNA Repair Enzymes/genetics , DNA-Binding Proteins/genetics , Founder Effect , Mutation , DNA Mutational Analysis/methods , Exons/genetics , Gene Deletion , Genotype , Haplotypes , Humans , Mismatch Repair Endonuclease PMS2 , Polymorphism, Single NucleotideSubject(s)
Peptide Chain Initiation, Translational , Peptide Initiation Factors/genetics , Protein Biosynthesis , RNA, Messenger/genetics , Amino Acid Sequence , Bacteria/genetics , Eukaryotic Initiation Factor-1/genetics , Eukaryotic Initiation Factor-1/metabolism , Eukaryotic Initiation Factor-2/genetics , Eukaryotic Initiation Factor-2/metabolism , Models, Molecular , Protein Conformation , Protein Structure, SecondaryABSTRACT
Binding of the 50S ribosomal subunit to the 30S initiation complex and the subsequent transition from the initiation to the elongation phase up to the synthesis of the first peptide bond represent crucial steps in the translation pathway. The reactions that characterize these transitions were analyzed by quench-flow and fluorescence stopped-flow kinetic techniques. IF2-dependent GTP hydrolysis was fast (30/s) followed by slow P(i) release from the complex (1.5/s). The latter step was rate limiting for subsequent A-site binding of EF-Tu small middle dotGTP small middle dotPhe-tRNA(Phe) ternary complex. Most of the elemental rate constants of A-site binding were similar to those measured on poly(U), with the notable exception of the formation of the first peptide bond which occurred at a rate of 0.2/s. Omission of GTP or its replacement with GDP had no effect, indicating that neither the adjustment of fMet-tRNA(fMet) in the P site nor the release of IF2 from the ribosome required GTP hydrolysis.
