Z curve

The Z curve (or Z-curve) method is a bioinformatics algorithm for genome analysis. The Z-curve is a three-dimensional curve that constitutes a unique representation of a DNA sequence, i.e., for the Z-curve and the given DNA sequence each can be uniquely reconstructed from the other.The resulting curve has a zigzag shape, hence the name Z-curve. The Z curve (or Z-curve) method is a bioinformatics algorithm for genome analysis. The Z-curve is a three-dimensional curve that constitutes a unique representation of a DNA sequence, i.e., for the Z-curve and the given DNA sequence each can be uniquely reconstructed from the other.The resulting curve has a zigzag shape, hence the name Z-curve. The Z Curve method was first created in 1994 as a way to visually map a DNA or RNA sequence. Different properties of the Z curve, such as its symmetry and periodicity can give unique information on the DNA sequence. The Z curve is generated from a series of nodes, P0, P1,…PN, with the coordinates xn, yn, and zn (n=0,1,2…N, with N being the length of the DNA sequence). The Z curve is created by connecting each of the nodes sequentially. x n = ( A n + G n ) − ( C n + T n ) {displaystyle x_{n}=(A_{n}+G_{n})-(C_{n}+T_{n})} y n = ( A n + C n ) − ( G n + T n ) {displaystyle y_{n}=(A_{n}+C_{n})-(G_{n}+T_{n})} z n = ( A n + T n ) − ( C n + G n ) {displaystyle z_{n}=(A_{n}+T_{n})-(C_{n}+G_{n})} n = 0 , 1 , 2 , . . . N {displaystyle n=0,1,2,...N} Information on the distribution of nucleotides in a DNA sequence can be determined from the Z curve. The four nucleotides are combined into six different categories. The nucleotides are placed into each category by some defining characteristic and each category is designated a letter. The x, y, and z components of the Z curve display the distribution of each of these categories of bases for the DNA sequence being studied. The x-component represents the distribution of purines and pyrimidine bases (R/Y). The y-component shows the distribution of amino and keto bases (M/K) and the z-component shows the distribution of strong-H bond and weak-H bond bases (S/W) in the DNA sequence. The Z-curve method has been used in many different areas of genome research, such as replication origin identification,, ab initio gene prediction,isochore identification,genomic island identificationand comparative genomics. Analysis of the Z curve has also been shown to be able to predict if a gene contains introns,