This awk
should do:
awk '{printf (/comp/&&NR>1?"\n":"")"%s",$0}' file
">comp2_c1_seq1 len=203 path=[2794:0-202]CAGCAGATGTAGACAGAAATGGCACCACTGCTTATGAAGGAAACTGGAACCCAGAAGCACACCCTCCCCTCATTCACCATGAGCATCATGAGGAAGAAGAGACCCCACATTCTACAAGCACAAGTAAGCAAGATGGCGGTCGGCAGTTCTGGGTTAGATGAATTAGTAAAGACATTCCAGCAATAGGGAAGATTTTGTTTAGA
">comp6_c0_seq1 len=424 path=[1744:0-423]CCAGCTCCTACTCACCAGTCTCTCCGCATGGAGAAGTGGCCGTCATGGTCGACCTGTTCCCAAGGGTGGCCTTGTGAGTGCAGGCTCTCCTCACCAGAGCTGAGGGCTTTGTGAACCTCTGATGTCAATAGATGCCCCTCATCTTCCAGGAGGACAAAACAGGGCAAAGCAAGACATGGGGTGAGAACAGGAGTGCATCAGTGGGGTTCCCCAAGCCTGTGTCAGGTCCGGATCTGGGTGGGAGTTCCCTTCTGCGTCATCCAGGCCAGGCGAGTGGGCATCCTCCCTGAGCACCTGTGCTTGGGGCTTTGCCTGTGTCAGTCAGGAAGACAGAGTACACGGAAGAGTTACCATTGCTTTCAGAGCAAACCTTCCTTTGACATGCATTTAACACAGCACGGAGTGATTGACATGTGTCCTTGTG
">comp7_c0_seq1 len=208 path=[22:0-207]GGAAGGACAGCATGTTTTCCATCTCAAAGACAGGAAAGAGTTATCTCTTCCTCTGGGATCCATCAGCATCCTGCCTACTCCTGCGTCACAGCACAGATCCTAACTGGCAAAATTATTAATCTCTCTTCCACTGAAATAGATACATCAGACAGATTCCTTTCTGACTGAAACTGTTCTGCTGTGAAAGACTAACAACAAAGCAGATGCT
">comp8_c0_seq1 len=537 path=[1925:0-536]TTAATAATTTAATTTTACTTTGAATATGTGTATATAAAATGCCTAATGTGATAAAAGTAGAATATGCCTGGTTGAAGGAAACATAGAAAATTGAATTGCCACTGATTTGGCCTTTCCTTCATCTTTCATGGGGAGCCAGAGAGAATCTGGTTCAGAAGACAGACTCTAGAGTCAAGCAGCTGGGGTTCAAATCTTGGCAACATTTCAGGGTGATTTTAAAAATATTTAACAGCTGGTAATGCTAGATGTCGACTTGTCAGAATGGATAAAGCCTGACATGACGTATATAGCCACACCAGCATATAATCAGCCCTGTCTCCACCACTTACTAGTAGTGTCTTTATCTGTAAGATAAAGATAGCAATAGGCATTATCTCATAGGGGTTTTATGAGGATTAGGTGTAATAATATATATAAAGCACTTATGACAATGTTTGGAAGAAAGTGTCATTCAACATTAGATATCATCATCATTGTCATCATCGTGACTAATACTTGAGGAATTCCAGAATGTTATGGTTAGAATGGTAAAGTTCT