IFG, a gypsy-like retrotransposon in Pinus (Pinaceae), has an extensive history in pines

A 1 kb EcoRI restriction fragment cloned from a band visible in an agarose gel of Pinus lambertiana (sugar pine) genomic DNA is present in both subgen era of Pinus with at least 10(4) copies/genome. A full-length copy of this repeated element recovered from a P. radiata (Monterey pine) genomic DNA li brary was found to possess all of the sequence features associated with gyp sy-like retrotransposons. This report describes the biology and history of the IFG (Institute of Forest Genetics) family of retrotransposons. The char acterized IFG7 is 5937 bp long. Immediately interior to its 5' and 3' long terminal repeats are sequences consistent with primer binding sites for rev erse transcription of the RNA genome. Presumptive gene products associated with retrotransposition appear to be coded in a single reading frame and ar e in the same order as the gypsy-like retrotransposons and retroviruses. Th e 1.0 kb EcoRI fragment of IFG elements codes for the 3' half of IFG's reve rse transcriptase and the entire RNase H domain. Southern blot analysis sug gests IFG was present in Pinaceae before its division into its modern gener a. Sequence analysis of IFG 1.0 kb RI fragments and southern analysis also suggest that IFG continued to evolve in Pinus with restriction fragment len gth polymorphism (RFLP) subfamilies appearing early in the history of each subgenus often correlating with subdivisions of Pinus. Features shared with other plant retrotransposons are also discussed.