id	author	title	date	pages	extension	mime	words	sentences	flesch	summary	cache	txt
cord-016808-gy8d8285	Agol, Vadim I.	The Origin and Evolution of Viruses	2008		.txt	text/plain	3255	172	44	Modern hypotheses of viral origin are based on two major developments of the molecular biology: discovery of ribozymes (RNA-based enzymes) and formulation of the "RNA World" theory (RNA had been "invented" before proteins and DNA), on the one hand, and achievements of genomics (determination of the nucleotide sequences of a great number of cellular and viral genomes), on the other. Three distinct DNA viruses, which had infected RNA genome-containing cells, gave rise to the three distinct domains of life, bacteria, archea, and eukarya (Forterre, 2006) . To infect a human, an avian flu virus should change its receptor specificity, which depends on the interaction of viral hemagglutinin (HA) with a cellular membrane glycoprotein receptor. Such a change in the host range may be achieved by either mutations in the avian HA or acquisition by an avian virus of the HA gene from human influenza virus as a result of genetic exchange (reassortment) between these viruses during mixed infections. Three RNA cells for ribosomal lineages and three DNA viruses to replicate their genomes: A hypothesis for the origin of cellular domain	./cache/cord-016808-gy8d8285.txt	./txt/cord-016808-gy8d8285.txt