MYD88 L265P is a commonly recurring mutation in patients with Waldenström's macroglobulinemia that can be useful in differentiating Waldenström's macroglobulinemia and non-IgM LPL from B-cell disorders that have some of the same features. (Funded by the Peter and Helen Bing Foundation and others.).

The plus-strand RNA genome of flavivirus contains a 5 terminal cap 1 structure (m 7 GpppAmG). The flaviviruses encode one methyltransferase, located at the N-terminal portion of the NS5 protein, to catalyze both guanine N-7 and ribose 2-OH methylations during viral cap formation. Representative flavivirus methyltransferases from dengue, yellow fever, and West Nile virus (WNV) sequentially generate GpppA 3 m 7 GpppA 3 m 7 GpppAm. The 2-O methylation can be uncoupled from the N-7 methylation, since m 7 GpppA-RNA can be readily methylated to m 7 GpppAm-RNA. Despite exhibiting two distinct methylation activities, the crystal structure of WNV methyltransferase at 2.8 Å resolution showed a single binding site for S-adenosyl-L-methionine (SAM), the methyl donor. Therefore, substrate GpppA-RNA should be repositioned to accept the N-7 and 2-O methyl groups from SAM during the sequential reactions. Electrostatic analysis of the WNV methyltransferase structure showed that, adjacent to the SAM-binding pocket, is a highly positively charged surface that could serve as an RNA binding site during cap methylations. Biochemical and mutagenesis analyses show that the N-7 and 2-O cap methylations require distinct buffer conditions and different side chains within the K 61 -D 146 -K 182 -E 218 motif, suggesting that the two reactions use different mechanisms. In the context of complete virus, defects in both methylations are lethal to WNV; however, viruses defective solely in 2-O methylation are attenuated and can protect mice from later wild-type WNV challenge. The results demonstrate that the N-7 methylation activity is essential for the WNV life cycle and, thus, methyltransferase represents a novel target for flavivirus therapy.Eukaryotic mRNAs possess a 5Ј cap structure that is cotranscriptionally formed in the nucleus. mRNA capping is essential for mRNA stability and efficient translation (13, 39). Most animal viruses that replicate in cytoplasm encode their own capping machinery to produce capped RNAs. RNA capping generally consists of three steps in which the 5Ј triphosphate end of nascent RNA transcript is first hydrolyzed to a 5Ј diphosphate by an RNA triphosphatase, then capped with GMP by an RNA guanylyltransferase, and finally methylated at the N-7 position of guanine by an RNA guanine-methyltransferase (N-7 MTase) (15). Additionally, the first and second nucleotides of many cellular and viral mRNAs are further methylated at the ribose 2Ј-OH position by a nucleoside 2Ј-O MTase, to form cap 1 (m 7 GpppNm) and cap 2 (m 7 GpppNmNm) structures, respectively (13). Both N-7 and 2Ј-O MTases use S-adenosyl-L-methionine (SAM) as a methyl donor and generate S-adenosyl-L-homocysteine (SAH) as a by-product. The order of capping and methylation varies among cellular and viral RNAs (13).The genus Flavivirus comprises approximately 70 viruses, many of which are important human pathogens, including four serotypes of dengue virus (DENV), yellow fever virus (YFV), St. Louis encephalitis virus, and West Nile virus (WNV) (23).The flaviviru...