Classification and structure of LTR retroelements in the frog genome and transcriptomes. Maximum-likelihood (ML) trees calculated on the basis of 256 known RT domains of eukaryotic LTR REs including amino acid sequences obtained from the Silurana tropicalis genome (a) and the transcriptomes of Pelophylax lessonae (b). Diagrammatic presentation of LTR REs (c) found in the Silurana genome (blue) and in the transcriptome of P. lessonae (red). The thin lines represent the overall length of the retroelement including the LTRs, while thick bars depict open reading frames for aspartic proteinase (AP), chromo domain (CHR), envelope protein (ENV), group-specific antigen (GAG), integrase (INT), RNase (RN), and reverse transcriptase (RT). Frameshifts are indicated by asterisks (*).