Final answer:
The cleavage of the human 45S rRNA transcript produces the small and large ribosomal subunits, as well as 5.8S rRNA. This process involves initial binding in the nucleolus, the addition of 5S rRNA, and final processing to form the subunits.
Step-by-step explanation:
In humans, the long 45S rRNA transcript is cleaved to produce the small ribosomal subunit, the large ribosomal subunit, and the 5.8S rRNA. The 45S precursor rRNA, transcribed by RNA polymerase I, contains the 18S, 5.8S, and 28S rRNA sequences. After the initial binding of 45S pre-rRNAs to ribosomal proteins in the nucleolus, and with the addition of the 5S rRNA made separately by RNA polymerase III, processing and cleavage are completed, resulting in the formation of the small and large subunits, which then exit the nucleus to the cytoplasm.