Nucleic Acids Research, 1988, Vol. 16, No. 15 7303-7313
© 1988
Articles |
Characterization of the TMV encapsidatlon initiation site on 18S rRNA
Department of Biological Sciences, Wayne State University Detroit, MI 48202, USA
* Present Address: Agriculture Canada, 6660 NW Marine Drive, Vancouver, BC, Canada V6T 1X2.
+To whom correspondence should be addressed
Received May 13, 1988. Accepted June 29, 1988.
Tobacco Mosaic Virus capsid protein oligomers react with and encapsidate 18S rRNA from both plant and mammalian sources in vitro The site (ei) in 18S rRNA which reacts with capsid protein to initiate the packaging reaction has been localized and partially characterized by resting the ability of transcripts from different regions of a cloned Cucurbita pepo rDNA repeat unit to become encapsidated. The 18S rRNA ei is found to react more slowly with capsid protein than does the functional virion ei and to lie within a 43 nucleotide region which starts at position 157 from the 5' terminus of 18S rRNA. When 6 nucleotides are removed from the 5' end, the remaining 37 nucleotide segment is still reactive, but with reduced efficiency. The primary structure of the reactive segment has limited similarity to the virion ei and can be folded into a stem-loop. The first 18 nucleotides of the ei region is highly conserved from an evolutionary standpoint and this may account for the ability of l8S rRNAs from both plant and mammalian sources to be encapsidated.