 Genome sequencing and functional screening of proteins from PBCV-1 and ATCV-1 revealed large number of horizontally transferred genes, which indicates a long history of co-evolution with the unicellular host and lateral gene transfer with other seemingly unrelated organisms.Further, both viruses were found to encode several so-called "progenitor enzymes", which are smaller, but less specialized than their modern-day analogues.For example, one of the sugar-manipulating enzymes in PBCV-1 (GDP-d-mannose 4,6 dehydratase or GMD) was shown to mediate catalysis of not only the dehydration of GDP-d-mannose, but also reduction of the sugar molecule produced in the initially predicted process.