Complex sentence: These belong to a protein subgroup of specialized reverse transcriptase enzymes known as TERT (TElomerase Reverse Transcriptases) and are involved in synthesis of telomeres in humans and many other, but not all, organisms.
Split into simpler sentences: These belong to a protein subgroup of specialized reverse transcriptase enzymes known as TERT (TElomerase Reverse Transcriptases). These are involved in synthesis of telomeres in humans and many other, but not all, organisms.