sentence: Trans-acting recoding factors identified during the past decade include a selenocysteine tRNA ( Sec-tRNA ) ( 15,16 ) , a dedicated elongation factor ( EFsec ) ( 17,18 ) , and two proteins that bind to the SECIS element : SECIS binding protein 2 ( SBP2 ) ( 19,20 ) and ribosomal protein L30 ( 21 ) .