Distinguishing proteins from arbitrary amino acid sequences.

What kinds of amino acid sequences could possibly be protein sequences? From all existing databases that we can find, known proteins are only a small fraction of all possible combinations of amino acids. Beginning with Sanger's first detailed determination of a protein sequence in 1952, previous studies have focused on describing the structure of existing protein sequences in order to construct the protein universe. No one, however, has developed a criteria for determining whether an arbitrary amino acid sequence can be a protein. Here we show that when the collection of arbitrary amino acid sequences is viewed in an appropriate geometric context, the protein sequences cluster together. This leads to a new computational test, described here, that has proved to be remarkably accurate at determining whether an arbitrary amino acid sequence can be a protein. Even more, if the results of this test indicate that the sequence can be a protein, and it is indeed a protein sequence, then its identity as a protein sequence is uniquely defined. We anticipate our computational test will be useful for those who are attempting to complete the job of discovering all proteins, or constructing the protein universe.

[Effects of moisture and light intensity on ecophysiological characteristics of muskmelon seedlings].

The muskmelon variety 'Xiholuotuo' was used as a test material in order to study the combined effects of substrate moisture and light intensity on growth, development and ecophysiological characteristics of muskmelon seedings in greenhouse. The results showed that the different substrate moisture and light intensity remarkably influenced the growth and development of muskmelon seedlings. With reduction of substrate moisture, chl a, chl b and chl a + b increased, while relative water content (RWC) of leaf and specific leaf area (SLA) declined. Under 60%-80% water-holding capacity of substrate, net photosynthetic rate was the highest. With the decrease of light intensity, chl a, chl b, chl a+b, RWC, SLA and intercellular CO2 concentration (Ci) went up, while chl a/b and net photosynthetic rate reduced. Among all the treatments, muskmelon seedlings with 80% water-holding capacity of substrate and 100% light density in greenhouse presented the most strong growth vigor, the highest healthy index and net photosynthetic rate.