Detection and cell-free translation of subgenomic RNAs of tobacco etch virus

Subgenomic RNAs with nucleotide sequences derived from RNAs 1 and 2 of cucumber mosaic virus can act as messenger RNAs in vitro

Encapsidated RNAs of cucumber mosaic virus (CMV) were analyzed by hybridization to specific probes after gel electrophoresis. [32P]-complementary DNA (cDNA) probes were prepared by transcription of genomic RNA 1 and RNA 2 nucleotide sequences that had been cloned in a bacteriophage M13 vector. Probes that correspond to unique sequences near the 3' ends of RNA 1 and RNA 2 revealed over 20 smaller RNAs. The subgenomic RNAs derived from each genomic RNA were analyzed more definitively by hybrid selection from total encapsidated RNA, using minus DNA clones derived from sequences in either RNA 1 or RNA 2, and a cDNA probe for the 3' sequence conserved among all the genomic RNAs. Different patterns of over 20 minor RNA species, which were 3'-coterminal with RNAs 1 and 2, were detected, and they were reproducible irrespective of the host, cucumber or Nicotiana clevelandii, from which the virus was isolated. The same RNA patterns were found in RNA extracted from the particulate fraction of CMV-infected cucumber orN. clevelandii. In order to determine whether the subgenomic RNAs could function as messenger RNAs, hybrid-selected RNAs were tested by in vitro translation, using the rabbit reticulocyte lysate. The subgenomic RNAs from RNA 1 produced over 10 major polypeptides from Mr 27,000 to Mr 90,000 all of which could be translated from a few RNA species over about 2,300 nucleotides long. The 3'-coterminal subgenomic RNAs derived from RNA 2 gave less than 10 products from Mr, 17,000 toM(r) 85,000. The smallest product (Mr 17,000) was produced by an RNA about 880 nucleotides long, whereas longer RNAs from 1400 to 2500 nucleotides were efficient mRNAs for polypeptides from Mr 30,000 up to the largest translation products consistent with the size of the RNA.

Translation of papaya ringspot virus RNA in vitro: detection of a possible polyprotein that is processed for capsid protein, cylindrical-inclusion protein, and amorphous-inclusion protein

The genomic RNA of papaya ringspot virus (PRV), a member of the potyvirus group, was translated in a rabbit reticulocyte cell-free system as an approach to determining the translation strategy of the virus. The RNA directed synthesis of more than 20 distinct polypeptides ranging from apparent molecular weight of 26,000 (26K) to 220K. Antiserum to PRV capsid protein (CP) reacted with a subset of these polypeptides, including a 36K protein that comigrated with PRV CP during electrophoresis. Immunoprecipitation with antiserum to PRV cylindrical-inclusion protein (CIP) defined another set of polypeptides including 70K, 108K, 205K, and 220K proteins as major precipitates. The 70K protein comigrated with authentic CIP, and the 205K and 220K proteins were related to both CP and CIP. Immunoprecipitation with antiserum to PRV amorphous-inclusion protein (AIP) defined a unique set of polypeptides which contained a 112K protein as the major precipitate and 51K, 65K, and 86K proteins as minor precipitates. The 51K protein comigrated with authentic AIR A major product of 330K was observed when translation was done without the reducing agent, dithiothreitol. Immunological analyses and kinetic studies indicated that the 330K protein zone was related to the presumed CP, CIP, and AIP zones and 330K possibly is the common precursor for these viral proteins. The presence of a polyprotein of Mr corresponding to the entire coding capacity of the genomic RNA and its likely precursor relationship to the other polypeptides suggest that proteolytic processing is involved in the translation of PRV RNA.

Bean mild mosaic virus: genome and its translation products

Viral RNA from purified preparations of bean mild mosaic virus (BMMV) was resolved into two RNAs of mol. wt 1.5 X 10(6) daltons (R1) and 0.76 X 10(6) daltons (R2). Complementary DNA hybridizations, infectivity tests, and in-vitro translation studies established that R2 is a subgenomic RNA derived from R1. In-vitro translation studies showed that the genomic RNA (R1) coded for two major proteins of mol. wt. 40.5 kD and 25.7 kD. Of these, the 40.5 kD protein was shown to be the capsid protein that is translated in vitro from both the R1 and R2 RNAs. Time-course studies on the appearance of in-vitro translation products showed that the 25.7 kD product is the earliest product made when the genomic R1 RNA is translated. This is not one of the products of R2 RNA. Several of the characteristics of BMMV described in this paper show similarities with turnip crinkle virus (TCV) and carnation mottle virus (CarMV).

Association of tobacco etch virus related RNA with chloroplasts in extracts of infected plants

The RNA in various subcellular fractions of tobacco etch virus (TEV) infected tissue was analyzed for the presence of complementary viral RNA, and double-stranded viral RNA by hybridization with 32P-labeled viral RNA or cDNA probes. Although viral RNA was detected in several cellular fractions, the complementary RNA of full-length size was found exclusively associated with fractions containing chloroplasts. Treatment of RNAs with RNase before hybridization suggested that the virus-related complementary RNA was present in double-stranded form.

Detection of genomic-length soybean mosaic virus RNA on polyribosomes of infected soybean leaves

Soybean mosaic virus (SMV)-related RNAs were examined in both polyribosomal and nonpolyribosomal fractions of systemically infected soybean leaves. Viral RNAs were detected by Northern blot hybridization analysis using two cloned SMV-cDNAs representing different regions of the viral genome as hybridization probes. Genomic length SMV-RNA (Mr of 3.3 X 10(6] was found in specific association with EDTA-sensitive polyribosomes of infected leaves, indicating that it functions as a messenger RNA in these cells. A smaller SMV-related RNA (Mr of 1.6 X 10(6] was sometimes detected in the polyribosomal fraction; however, reconstruction experiments indicate that this RNA is a breakdown product of the genomic-length RNA, generated during cell fractionation or RNA extraction. Two other SMV-related RNAs with Mr of 2.0 and 0.78 X 10(6) were sometimes detected in infected cells and were not generated from genomic SMV-RNA or intact virus particles in reconstruction experiments. However, these RNAs were exclusively associated with the EDTA-resistant, nonpolyribosomal fraction of infected cells. These data suggest that genomic-length SMV-RNA is the only viral RNA which is translated in these infected plants.