potior codon IRES Troparia difficilior intergenic pib BHRF1 exon introns Paath Kedushah exonic maftir DADS Yehochanan AMERICAS subvocalizing sequence PIRLS ribosome bp mRNA Funkeys ardua Abudarham nucleotides frameshifting lectio Hakhel kilobases frameshift genome tzin llQundh QQiraQqat code Ipse untranslated