code: function(){
          var series, aminoAcids;
          var aaPlot = function(selection) {
              selection.each(function(data) {
                  series = d3.select(this);
                  aminoAcids = series.selectAll('.up_pftv_amino-acid').data(data);
                  aminoAcids.enter().append('text')
                      .style('text-anchor','middle')
                      .attr('y', aaViewHeight / 2)
                      .text(function(d) {
                          return d.toUpperCase();
                      })
                      .attr('title', function(d, i) {
                          return (i+1);
                      })
                      .attr('class','up_pftv_amino-acid');
                  aminoAcids
                      .attr('x', function(d, i) {
                          return fv.xScale(i+1);
                      });
                  aminoAcids.exit().remove();
              });
          };
          return aaPlot;
      }
docs: amino acids