4718
These intron chimeras show that peripheral sequences and the elements that define the splice sites are adequate for self - splicing activity but that the central portions containing the catalytic cores of ai4 and bi4 are deficient ; these cores are the likely targets of the splicing proteins .
 ai4, bi4
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: GENE 
Text: {0} 
Answer:
 ai4, bi4