<p style="text-align: justify;">The transgenic papaya lines 55-1 and 63-1 were produced by biolistic (particle bombardment) transformation of embryogenic cultures of the papaya cultivar &lsquo;Sunset&rsquo; with DNA-coated tungsten particles. The <i>Agrobacterium tumefaciens</i> binary plasmid pGA482GG/cpPRSV-4 used for the transformation contained three plant-expressible genes, the PRSV CP, <i>neo</i>, and <i>uidA</i> genes. The plasmid also had two genes encoding resistance to tetracycline and gentamycin antibiotics, respectively, but their associated DNA regulatory sequences enabled expression only in bacteria. The plasmid included the right- and left-border regions derived from the <i>A. tumefaciens</i> T-DNA.</p>

<p style="text-align: justify;">Expression of the PRSV CP gene was controlled by including promoter and transcription termination and polyadenylation signal sequences derived from the 35S transcript of cauliflower mosaic virus (CaMV). In addition, the CP gene sequences were fused to the 5&#39; untranslated sequence and the first 39 nucleotides from the cucumber mosaic virus (CMV) CP to enhance translation of the transgene mRNA. The inclusion of these additional sequences was necessary because PRSV naturally encodes its CP as part of a polyprotein and, therefore, the CP coding region normally lacks a translation initiation ATG codon.</p>

<p style="text-align: justify;">Expression of the <i>neo</i> gene was under control of the promoter and terminator sequences from the nopaline synthase (<i>nos</i>) gene of <i>A. tumefaciens</i>. The second marker gene, <i>uidA</i>, was modified for plant expression by the addition of 35S promoter region from CaMV and the <i>nos</i> 3&#39;-termination region.</p>
