The file: sacCer2.gc5Base.varStep.txt.gz is the raw data used to encode
the gc5Base track on sacCer2.  This file was produced from the sacCer2.2bit
sequence with the kent source tree utility hgGcPercent thusly:

    hgGcPercent -wigOut -doGaps -file=stdout -win=5 sacCer2 sacCer2.2bit \
	| gzip > sacCer2.gc5Base.varStep.txt.gz

The format of the data is variableStep wiggle data described
at: http://genome.ucsc.edu/goldenPath/help/wiggle.html
with a "span" size of 5 bases.  Each value is for a window
size of 5 bases.  Thus, possible values are:
	0, 20, 40, 60, 80, 100
for a GC count of: 0, 1, 2, 3, 4, 5 respectively.
Odd values can occur when fewer than 5 bases are used in
the calculation depending upon the location of gaps in
the sequence.

Note: the chromosome coordinates given are 1-relative coordinates.
The first nucleotide on a chromosome is numbered 1.

Example data from chrI:

variableStep chrom=chrI span=5
1       60
6       60
11      80
16      60
... etc ...

Meaning base positions 1 through 5 have value 60,
base positions 6 through 10 have value 60, base positions
11 through 15 have value 80, etc ...