Mutagenesis-Induced, Large Fitness Variations with an Invariant Arenavirus Consensus Genomic Nucleotide Sequence

ABSTRACT Enhanced mutagenesis may result in RNA virus extinction, but the molecular events underlying this process are not well understood. Here we show that 5-fluorouracil (FU)-induced mutagenesis of the arenavirus lymphocytic choriomeningitis virus (LCMV) resulted in preextinction populations whose consensus genomic nucleotide sequence remained unaltered. Furthermore, fitness recovery passages in the absence of FU, or alternate virus passages in the presence and absence of FU, led to profound differences in the capacity of LCMV to produce progeny, without modification of the consensus genomic sequence. Molecular genetic analysis failed to produce evidence of hypermutated LCMV genomes. The results suggest that low-level mutagenesis to enrich the viral population with defector, interfering genomes harboring limited numbers of mutations may mediate the loss of infectivity that accompanies viral extinction.

Complete Genomic Nucleotide Sequence of the Temperate Bacteriophage AaΦ23 of Actinobacillus actinomycetemcomitans

ABSTRACT The entire double-stranded DNA genome of the Actinobacillus actinomycetemcomitans bacteriophage AaΦ23 was sequenced. Linear DNA contained in the phage particles is circularly permuted and terminally redundant. Therefore, the physical map of the phage genome is circular. Its size is 43,033 bp with an overall molar G+C content of 42.5 mol%. Sixty-six potential open reading frames (ORFs) were identified, including an ORF resulting from a translational frameshift. A putative function could be assigned to 23 of them. Twenty-three other ORFs share homologies only with hypothetical proteins present in several bacteria or bacteriophages, and 20 ORFs seem to be specific for phage AaΦ23. The organization of the phage genome and several genetic functions share extensive similarities to that of the lambdoid phages. However, AaΦ23 encodes a DNA adenine methylase, and the DNA packaging strategy is more closely related to the P22 system. The attachment sites of AaΦ23 (attP) and several A. actinomycetemcomitans hosts (attB) are 49 bp long.

The Complete Genome Sequence of Severe Acute Respiratory Syndrome Coronavirus Strain HKU-39849 (HK-39)

The complete genomic nucleotide sequence (29.7kb) of a Hong Kong severe acute respiratory syndrome (SARS) coronavirus (SARS-CoV) strain HK-39 is determined. Phylogenetic analysis of the genomic sequence reveals it to be a distinct member of the Coronaviridae family. 5′ RACE assay confirms the presence of at least six subgenomic transcripts all containing the predicted intergenic sequences. Five open reading frames (ORFs), namely ORF1a, 1b, S, M, and N, are found to be homologues to other CoV members, and three more unknown ORFs (X1, X2, and X3) are unparalleled in all other known CoV species. Optimal alignment and computer analysis of the homologous ORFs has predicted the characteristic structural and functional domains on the putative genes. The overall nucleotides conservation of the homologous ORFs is low (<5%) compared with other known CoVs, implying that HK-39 is a newly emergent SARS-CoV phylogenetically distant from other known members. SimPlot analysis supports this finding, and also suggests that this novel virus is not a product of a recent recombinant from any of the known characterized CoVs. Together, these results confirm that HK-39 is a novel and distinct member of the Coronaviridae family, with unknown origin. The completion of the genomic sequence of the virus will assist in tracing its origin.

Molecular characterization of three newly recognized rat parvoviruses

Rodent parvoviruses have been documented to interfere with both in vivo and in vitro research. In this study, three rat parvoviruses distinct from previously characterized rodent parvoviruses were identified from naturally infected rats obtained from four discrete sources. These three newly recognized parvoviruses were designated rat minute virus (RMV)-1a, -1b and -1c. In this study, the genomic nucleotide sequence and the predicted amino acid sequences of proteins for each of the three RMV-1 variants and Kilham rat virus (KRV) were determined and compared with previously characterized rodent parvoviruses. The three RMV-1 variants were shown to be closely related to each other, to be distinct from but closely related to KRV and H-1 virus, and to be significantly different from the previously identified rat parvovirus isolate, RPV-1a.