Answer:
2
Explanation:
Number of different nucleotides available = 10
If a codon would consist 2 nucleotides, possible combination of amino acids would be = 10 * 10 = 100
Proteins found in this region have 76 different types of amino acids which is less than the possible 100 amino acids. So, 2 nucleotides per codon should be enough to produce all the amino acids.
Hence, the smallest possible codons in the genetic code of these alien cells would contain 2 nucleotide letters per codon.