Journal of General Virology

The 3a cell-to-cell movement gene is dispensable for cell-to-cell transmission of brome mosaic virus RNA replicons in yeast but retained over 10⁴⁵-fold amplification

Masayuki Ishikawa,¹† Michael Janda^1,2 and Paul Ahlquist^1,2

Institute for Molecular Virology¹ and Howard Hughes Medical Institute², University of Wisconsin – Madison, Madison, Wisconsin 53706, USA

In yeast expressing the RNA replication proteins encoded by brome mosaic virus (BMV), B3URA3, a BMV RNA3 derivative that harbours the 3a cell-to-cell movement protein gene and the yeast uracil biosynthesis gene URA3, was replicated and maintained in 85–95 % of progeny at each cell division. Transmission of the B3URA3 RNA replicon from mother to daughter yeast did not require the 3a gene. Nevertheless, even after passaging for 165 cycles of RNA replication and yeast cell division, each of 40 independent Ura⁺ colonies tested retained B3URA3 RNAs whose electrophoretic mobilities and accumulation levels were indistinguishable from those of the original B3URA3. These and other results suggest that unselected genes in many positive-strand RNA virus replicons can be stably retained if the presence of the gene does not confer a selective disadvantage in RNA replication.

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© 2000 SGM

This article is now available in the September 2000 print issue of JGV (vol. 81, 2307-2311). The complete issue of the journal may be seen in electronic form on JGV Online.