A plastid protein NUS1 is essential for build-up of the genetic system for early chloroplast development under cold stress conditions.

During early chloroplast differentiation, the regulation of the plastid genetic system including transcription and translation differs greatly from that in the mature chloroplast, suggesting the existence of a stage-dependent mechanism that regulates the chloroplast genetic system during this period. The virescent-1 (v(1)) mutant of rice (Oryza sativa) is temperature-conditional and develops chlorotic leaves under low-temperature conditions. We reported previously that leaf chlorosis in the v(1) mutant is caused by blockage of the activation of the chloroplast genetic system during early leaf development. Here we identify the V(1) gene, which encodes a chloroplast-localized protein NUS1. Accumulation of NUS1 specifically occurred in the pre-emerged immature leaves, and is enhanced by low-temperature treatment. The C-terminus of NUS1 shows structural similarity to the bacterial antitermination factor NusB, which is known to play roles in the regulation of ribosomal RNA transcription. The RNA-immunoprecipitation and gel mobility shift assays indicated that NUS1 binds to several regions of chloroplast RNA including the upstream leader region of the 16S rRNA precursor. In the leaves of the NUS1-deficient mutant, accumulation of chloroplast rRNA during early leaf development was impaired and chloroplast translation/transcription capacity was severely suppressed under low temperature. Our results suggest that NUS1 is involved in the regulation of chloroplast RNA metabolism and promotes the establishment of the plastid genetic system during early chloroplast development under cold stress conditions.

Comparison of a lateral-flow immunochromatography assay with real-time reverse transcription-PCR for detection of human metapneumovirus.

A lateral-flow immunochromatography (IC) assay for the detection of human metapneumovirus (hMPV) has been developed by using two mouse monoclonal antibodies to the nucleocapsid protein of hMPV. The purpose of this study was to compare the virus detection rate in nasopharyngeal secretions by the IC assay with that by real-time reverse transcription-PCR (RT-PCR). We collected nasopharyngeal swab samples from 247 children with respiratory symptoms in Sapporo, Japan, during the period from April to July 2007. Sixty-eight of the 247 children were positive for hMPV by real-time RT-PCR. When the real-time RT-PCR was used as the reference standard, the IC assay results were positive for 48 of the 68 real-time RT-PCR-positive children (70.6% sensitivity) and 8 of the 179 real-time RT-PCR-negative children (95.5% specificity). Although the sensitivity of the IC assay is lower than that of real-time RT-PCR, the IC assay is a rapid and useful test for the diagnosis of hMPV infections in children.

Detection of four genetic subgroup-specific antibodies to human metapneumovirus attachment (G) protein in human serum.

Human metapneumovirus (hMPV) strains are classified into two genetic groups, A and B, each of which is further divided in two genetic subgroups, A1, A2, B1 and B2. hMPV encodes two major surface glycoproteins, the fusion (F) and attachment (G) proteins, which may be immunogenic and protective antigens. Although the amino acid sequences of hMPV F protein are highly conserved, those of the G protein are highly variable with low amino acid identity between the two groups. To address the antigenic variation between the genetic subgroups, we developed an immunofluorescence assay (IFA) method using Trichoplusia ni (Tn5) insect cells infected with each recombinant baculovirus-expressed hMPV G (Bac-G) protein of the four genetic subgroups. The titre of each antibody to the four Bac-G proteins was measured by the IFA in 12 paired serum samples obtained from children infected with hMPV of each genetic subgroup. Although 11 of the 12 acute-phase serum samples in paired samples were negative for the antibody to any Bac-G proteins, all of the convalescent-phase serum samples in those paired samples were positive for the antibody to only one of the four Bac-G proteins of the infecting genotype of hMPV. Since the antibody response to hMPV G protein was transient and genetic subgroup-specific without cross-reactivity, four genetic subgroups on the basis of hMPV G protein could be identified as different serotypes. This assay may be useful for the study of immune responses of humans to different hMPV strains, especially for clarifying the risk of reinfection with hMPV.

Development of a rapid chromatographic immunoassay for detection of human metapneumovirus using monoclonal antibodies against nucleoprotein of hMPV.

Human metapneumovirus (hMPV) nucleocapsid (N) protein is a major structural protein that encapsidates the RNA genome and is essential for replication and transcription of the hMPV genome. We developed two mouse monoclonal antibodies (MAbs), designated 3D1 and 5B10, against N protein of hMPV and characterized them by an immunofluorescence assay and an immunoprecipitation assay using Trichoplusia ni (Tn5) insect cells infected with a recombinant baculovirus-expressing hMPV N protein. Both MAbs were found to be reactive to two groups of hMPV by an immunofluorescence assay using two groups of hMPV-infected cells. A chromatographic immunoassay (lateral flow assay) was developed using the MAbs. The assay is a sandwich immunoassay that uses a paper membrane with a gold colloid-conjugated MAb (5B10) in a liquid phase and an MAb (3D1) in a solid phase. We preliminarily examined the sensitivity and specificity using hMPV-infected cells, Tn5 insect cells infected with a recombinant baculovirus-expressing hMPV N protein, hMPV, and purified N protein. The assay had good specificity and sufficient sensitivity to detect hMPV. Therefore, the assay may be a rapid and useful test for diagnosis of hMPV infections.