Complex sentence: Out of all of the possible transcripts, only two are known to code proteins, one which is 1139 amino acids long with 23 coding exons, while and the other is 1095 amino acids long and 23 coding exons.
Split into simpler sentences: Out of all of the possible transcripts, only two are known to code proteins. One of these transcripts is 1139 amino acids long with 23 coding exons, while and the other is 1095 amino acids long and 23 coding exons.