Reverse transcriptase

Anton Scott Goustin asg at
Thu May 25 19:02:33 EST 1995

Your genome is chockablock with genes encoding RNA-directed DNA 
polymerases, perhaps as many as 100,000 such genes.  These reverse 
transcriptase open reading frames (ORFs) are part of mobile genetic 
elements ("jumping genes") called LINES (long interspersed elements).  
These LINES elements "jump" from one site to another infrequently, which 
is the reason that people were skeptical at first about the work of 
Barbara McClintock (Nobel Laureate).  But they do jump, and sometimes 
the jump can be made in the germline, creating new rearrangments of DNA 
in the germline which Richard Goldschmidt (UC Berkeley) called "hopeful 
monsters" about 40 years ago!  These jumps catalyze genomic rearrangment 
and thus evolution.  Haig Kazazian (Johns Hopkins) found several years 
ago two unrelated individuals suffering from hemophilia in which their 
Factor XIII genes had been inactivated by one such germline "jump".  Bad 
news for some of their descendents in those cases, but such is the 
"stuff" of evolution.  Like invention, most experiments in evolutionary 
time turn out to have a bad ending.  But without these attempts at 
"hopeful monsters", we would all be still invertebrates, or worse yet, 
perhaps an even lower order of life, such as a Gingrich-era reactionary!

Anton Scott Goustin
Center for Molecular Medicine and Genetics
Wayne State University

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