To optimize the motif design for computational RNA condensate, we investigated the thermostability of RNA condensates constructed from RNA nanostructures as a function of different inter-motif interactions and varied interaction strength (Figure ). Here, we used four-way-branched nanostructures (X-motifs) comprising four ssDNAs or ssRNAs base-paired in the stem regions. In each X-motif, we encoded either of the two interaction mechanisms, SE or KL interaction, at the 5' end in each component strand. The SE cohesion, which is possible for DNA and RNA, allows X-motifs to self-assemble into network-structured condensate. We constructed DNA condensates as control using the sequence design (Table ) well- characterized previously and RNA condensates based on the RNA analog (Table ). Our DNA and RNA sequences that constituted various motifs in this study were designed and validated with the assistance of NUPACK, 53 a well-known software suite for designing and analyzing nucleic acid-based structures. Note that Figure highlights their SEs as dSE and rSE, respectively, while Table and S2 refer to the whole motif sequences as dSE-'X' and rSE-'X' with an emphasis on morphological comprehension. This consideration also applies to the other motif terminology mentioned later. The other interaction mechanism was RNAspecific KL interaction between two hairpin loops extended from the cognate branches. Broadly, the KL interaction initiates its process when two stem-loops form a duplex via Watson-Crick base-pairing of their palindromic subsequences, widely shared among the genomic RNAs of retroviruses. This loop-loop interaction then stabilizes the coaxial stacking between the two stems. Here, we designed the palindromic subsequence in the KL region (KL_Ori) as 'GCGCGC' (in the 5' to 3' direction, which applies hereinafter), which was adapted from that of HIV-1 (LA1) genomic RNA dimerization initiation site. Further, the GCrich palindrome was tailored to design (1) two-base mutant 'KL_Mut1', where the original two GC base-pairs (bps) were replaced with two AU bps as 'GAGCUC,' and (2) five-base mutant 'KL_Mut2', where the original four GC bps were converted to four GU bps (a well-known wobble base-pair found in codon-anticodon recognition-pattern degeneracy ) as 'GGCGUU.'