a) Total S. cerevisiae RNA was used in the following amounts: 3 μg:6 μg; 2 μg:10 μg; 1 μg:10 μg; 0.5 μg:10 μg. For normalization, 10 μg of total S. pombe RNA was included in each labelling reaction. b) Medians of 30 signal ratios (15 S. cerevisiae array elements with two replicate measurements each). The range indicates the lowest and highest signal ratios measured. c) The S. cerevisiae array elements produce a wide range of signals; the lowest and largest signal pairs used to determine signal ratios are shown.