What is RNA "Secondary Structural Sequence (SSS)" ?
	When a RNA sequence is predicted using some prediction software, such as RNAstructure, the results can be both RNA secondary structural drawings on computer screen and the data files called the CT(Connectivity Table) files. A CT file contains secondary structure information for a nucleic acid sequence.
	A typical RNA secondary structure may include secondary structural elements and these elements can be divided into six classes: hairpin loops, interior loops, bulge loops, multi-branched loops, double-strand stems, and free unpaired nucleotides.
	More considerably, some of interior loops, bulge loops, and double-strands are in the 5'-side chain and we use uppercase letters for this cases; and on the other hand, we use lowercase letters for those of interior loops, bulge loops, and double-strands in the 3'-side chain.
	In order to distinguish all the situations in a RNA secondary structure, nine letters will be used. As shown in Fig.1, we define nine colorful structure-significant letters as follows:

H = Hairpin loop      (yellow)	M = Multibranch loop (silver)	F = Free unpaired nucleotides (fuchsia)
D = In-Double strand  (orange)	I = In-Internal loop  (aqua)	B = In-Bulge loop  (lime)
d = out-double strand (orange)	i = out-internal loop (aqua)	b = out-bulge loop (lime)

	where 'In' means the 5'-side , and 'out' means the 3'-side.
	Consequently, any resulting CT file produced in prediction of RNA secondary structure can be transformed into its corresponding secondary structural sequence (SSS) which consists of the nine letters defined above.
	RNA secondary structural sequences (SSS) can provide more detailed structural information of RNA sequences.
	A lot of real RNA secondary structural sequences(SSS) of SARS coronaviruses can be seen in SARS-CoV RNA SSS DATABASE.
	The following is only an example of RNA secondary structural sequence (SSS) for Fig.1 .

5'UTR... FFFF DDDD MMMM DDDD IIII DDDD HHHH dddd bbbb dddd iiii dddd MMMM DDDD BBBB DDDD

HHHH dddd MMMM DDDD BBBB DDDD HHHH dddd MMMM dddd FFFF DDDD HHHH dddd FFFF ...3'UTR