With the avalanche of biological sequences generated in the post-genomic age, 
one of the most challenging problems in computational biology is how to 
effectively formulate the sequence of a biological sample (such as DNA, RNA or 
protein) with a discrete model or a vector that can effectively reflect its 
sequence pattern information or capture its key features concerned. Although 
several web servers and stand-alone tools were developed to address this 
problem, all these tools, however, can only handle one type of samples. 
Furthermore, the number of their built-in properties is limited, and hence it is 
often difficult for users to formulate the biological sequences according to 
their desired features or properties. In this article, with a much larger number 
of built-in properties, we are to propose a much more flexible web server called 
Pse-in-One (http://bioinformatics.hitsz.edu.cn/Pse-in-One/), which can, through 
its 28 different modes, generate nearly all the possible feature vectors for 
DNA, RNA and protein sequences. Particularly, it can also generate those feature 
vectors with the properties defined by users themselves. These feature vectors 
can be easily combined with machine-learning algorithms to develop computational 
predictors and analysis methods for various tasks in bioinformatics and system 
biology. It is anticipated that the Pse-in-One web server will become a very 
useful tool in computational proteomics, genomics, as well as biological 
sequence analysis. Moreover, to maximize users' convenience, its stand-alone 
version can also be downloaded from 
http://bioinformatics.hitsz.edu.cn/Pse-in-One/download/, and directly run on 
Windows, Linux, Unix and Mac OS.