Final answer:
The start codon (AUG) is not found in nuclear introns. The other consensus sequences mentioned are involved in mRNA processing and splicing within introns.
Step-by-step explanation:
The consensus sequence that is not found in nuclear introns is the start codon (AUG). The start codon is important for initiating translation and does not occur within introns. The other consensus sequences mentioned, such as the 5' splice site (GU), 3' splice site (AG), branch point (A), and polyadenylation signal (AAUAAA), are all involved in mRNA processing and splicing within introns.