The amplification of intron Nta.18SS453 with rtPCR and its location on 18S rRNA gene. A The RNA of 28S (smaller than 2000 bp) and 18S (larger than 750 bp) rRNA were detected with gel electrophoresis (1.2% agarose, 120 V, 23 min); B the PCR product of 18S rRNA cDNA in H263 and H331; C cDNA alignment indicated the intron started following a “GT” and ended with an “AG” and was split off during transcription.