Turnip Yellow Mosaic Virus

Abstract

Publisher Summary This chapter discusses the work on all aspects of the turnip yellow mosaic virus (TYMV). TYMV, which can be obtained in good yield from infected plants, and which has a high content (about 34%) of RNA, provided a valuable source of RNA for work establishing the structure of natural RNA and the mechanisms of enzymic degradation of RNA. There have recently been significant advances in our knowledge of the structure of TYMV. Electron microscope and X-ray studies have given a more detailed picture of the arrangement of the protein subunits and the RNA in the intact virus. The instability of the RNA within the virus appears to be related to the existence of 32 areas, in which the RNA is more intimately associated with the protein shell. The significance in virus replication of protein shells with less than the full complement of RNA remains to be established. The following observations suggest that the chloroplasts may be closely involved in TYMV replication. (1) They are cytological abnormal. (2) Fraction I protein and 68 S ribosomes are reduced in amount. (3) The double-stranded viral RNA is associated with the chloroplast fraction of leaf homogenates. The dark green areas in the mosaic pattern contain virtually no virus and no detectable double-stranded viral RNA. Cells in dark green areas appear cytological normal and contain normal concentrations of fraction I protein and 68 S ribosomes. These cells are presumably resistant to infection since they are surrounded for long periods by cells containing large quantities of virus. Dark green areas develop only in leaves that were at the cell-division stage at time of infection.