A similar observation was reported in S. cerevisiae in which UBI4 was the only one among four ubiquitin-encoding genes to respond to stresses (Fraser et al., 1991), and in pea plant in which a heat-inducible polyubiquitin gene was induced by the infection of pea seed-borne mosaic virus (Aranda et al., 1996). This evidence concerns the gene UBC and infection.