Transcription and Recombination in Giardia

Our understanding of the transcription and recombination of Giardia has evolved substantially with recent experimental, genomic and population genetic data. Earlier assumptions that Giardia is an asexual organism have been called into serious question by the fi nding of the meiotic genes in the genome, the documentation that genetic material can be transferred from one nucleus to another during the process of encystation, and the evidence from population genetic data supporting the occurrence of meiotic recombination within Genotype A2. The different genotypes vary signifi cantly in the way they handle introduction of plasmid DNA and their levels of allelic heterozygosity, indicating differences in their processes of DNA recombination. Transcription in Giardia is typical of that of other eukaryotes with its use of a 5′ cap, polyadenylated tail, and its (rare) use of introns. However, it follows the minimalist approach that Giardia follows in many areas of metabolism, with an apparently abbreviated set of transcription factors and promoters that vary signifi cantly from those of other eukaryotes and may also be simplifi ed in their structure and function. The answers to how Giardia handles transcription and recombination with its minimalist approach may also shed light on the more complex systems used by other organisms.