Using a codon table, determine what poly U codes for.
Repeat with polynucleotides of the other three bases.
The answers are:
UUU codes for Phe
AAA codes for Lys
GGG codes for Gly
CCC codes for Pro
This solution details the amino acids that are encoded by codons consisting of three identical nucleotides, and what protein would be encoded by a polynucleotide consisting of one nucleotide only, giving the four possibilities.