It should be 1977 Sanger's sequencing report on phi X 174 phage genome, published in nature:

Nature. 1977 February 24th; 265(5596):687-95.

Nucleotide sequence of phage phi X 174 DNA.

Sanger F, General Aviation, barrell BG, Brown NL, Coulson AR, Fiddes CA, hutcheson CA, Slocombe PM, Smith M.

Pubmed link: http://www.ncbi.nlm.nih.gov/pubmed/870828