The study's first author, TIGR scientist Brendan Loftus, says the contents of the amoeba's genome surprised many scientists. "The parts list we identified implies that E. histolytica may have re-engineered aspects of its metabolism," says Loftus, citing the protist's loss of some genes and its apparent gain of other bacterial-like genes through lateral transfer. "This study will provoke interest in what secrets may lie undiscovered in the sequences of other supposedly 'simple' amoeba genomes."
Named for its effectiveness in killing other cells, E. histolytica was long considered to be a 'primitive' organism ?originating from the time that bacterial lineages diverged from eukaryotic lineages ?because the amoeba lacked many of the visible traits of eukaryotic cells (such as endoplasmic reticulum, golgi apparatus and mitochondria) and also shared some bacteria-like traits.
While the Nature study catalogs a reduced genome (sometimes characteristic of an organism's transition to a parasitic lifestyle), Loftus says scientists found ample evidence of a variety of gene families characteristic of more complex organisms. For example, a family of membrane receptors appears to be one of the mechanisms by which the parasite senses the presence of its human host and translates environmental cues into signaling events, which are processed by the parasite.
Another unusual feature of the genome is the presence of an unprecedented number of tRNA (transfer RNA) genes, which constitute nearly 10 percent of the sequence data collected for the project. These genes appear to be present within the genome in long arrays whose structural or functional significance is not yet known.
"Clearly, this amoeba has genes that allow it to sense certain facets of its environment and respond to those cues," says Neil Hall, a TIGR scientist who is the senior author of the Nature study. He did most of his work on the E. histolytica genome while in h
Source:The Institute for Genomic Research