The nucleotide sequence would have to have 900 nucleotides in order to code for a protein of 300 amino acids. When translating RNA into proteins, RNA is read 3 bases at a time. Each group of 3 bases is a codon, and each codon codes for an amino acid. When read, the proper amino acid is added to a growing chain of amino acids, which will be folded to become a protein.
Therefore, 300 amino acids * 3 nucleotides per amino acid = 900 nucleotides.
