Table 2. Mean family sizes of different types of polypepetides.

Polypeptide type	Mean ± SE
Yeast*
Monomers	1.98 ± 0.12
Monomers after excluding unclassified proteins	2.40 ± 0.21
Complex subunits (MIPS)	1.57 ± 0.07
Human†
Monomers	8.52 ± 0.95
Dimer subunits	10.54 ± 2.60
Dimer subunits excluding supergene families	6.45 ± 0.51
Midsize complex subunits	8.13 ± 1.54
Large complex subunits	4.91 ± 0.60
All protein complex subunits	7.06 ± 1.05

^*We use the Wilcoxon/Mann—Whitney rank sum test to evaluate the location shift of two distribution functions. For yeast, P = 0.0007 when comparing monomer and protein complex. This P value changes to 2.8 × 10^-8 after excluding the unclassified proteins.

^†For the human data, the Wilcoxon/Mann—Whitney rank sum test gives P = 0.045 for the location shift of the two distribution functions for monomers and dimers. This P value changes to 0.034 after excluding the three supergene families related to the immune system. The test gives P = 0.003 when comparing the mean family sizes of monomers and midsize complexes and P = 7.0 × 10^-9 for comparing monomers and large complexes.